Hematology

Radha Gajjar, MD, and Elizabeth Jalazo, MD

I. Anemia

Anemia is defined as a reduction in hemoglobin (Hb) two standard deviations below the mean, based on age-specific norms (Table 14-1 and Fig. 14-1). Evaluation should include:

1. Complete history, including nutrition, menstruation, ethnicity, fatigue, pica, medication exposure, growth and development, blood loss, hyperbilirubinemia and family history of anemia, splenectomy, or cholecystectomy.

2. Physical examination, including evaluation of pallor, tachycardia, cardiac murmur, jaundice, hepatosplenomegaly, glossitis, tachypnea, koilonychia, angular cheilitis or signs of systemic illness.

3. Initial laboratory tests including complete blood cell count (CBC) with red blood cell (RBC) indices (mean corpuscular volume [MCV], mean corpuscular hemoglobin [MCH], red cell distribution width [RDW]), reticulocyte count, stool for occult blood, urinalysis, and serum bilirubin. Complete evaluation always includes a peripheral blood smear.

B. Diagnosis

Anemias may be categorized as macrocytic, microcytic, or normocytic. Table 14-2 gives an approach to diagnosis based on RBC production as measured by reticulocyte count and cell size. Note that normal ranges for Hb and MCV are age dependent.

C. Evaluation of Specific Causes of Anemia

1. Iron-deficiency anemia: Hypochromic/microcytic anemia with a low reticulocyte count and an elevated RDW.

a. Serum ferritin reflects total body iron stores after age 6 months and is the first value to fall in iron deficiency; may be falsely elevated with inflammation or infection.

b. Other indicators: Low serum iron, elevated total iron-binding capacity (TIBC), low mean corpuscular hemoglobin concentration (MCHC), elevated transferrin receptor level, and low reticulocyte Hb content.

c. Iron therapy should result in an increased reticulocyte count in 2–3 days and an increase in hematocrit (HCT) after 1–4 weeks of therapy. Iron stores are generally repleted after 3 months of therapy.

d. Mentzer index (MCV/RBC): Index >13.5 suggests iron deficiency; expect elevated RDW. Mentzer index <11.5 suggests thalassemia minor; expect low/normal RDW.

FIGURE 14-1 Hemoglobin and mean corpuscular volume (MCV) by age and gender. (Data from Dallman PR, Siimes MA. Percentile curves for hemoglobin and red cell volume in infancy and childhood. J Pediatr. 1979;94:26.)

TABLE 14-1

Age-Specific Blood Cell Indices

Age	Hb (g/dL)^∗	HCT (%)^∗	MCV (fL)^∗	MCHC (g/dL RBC)^∗	Reticulocytes	WBCs (×10³/mL)^†	Platelets (10³/mL)^†
26–30 wk gestation^‡	13.4 (11)	41.5 (34.9)	118.2 (106.7)	37.9 (30.6)	—	4.4 (2.7)	254 (180–327)
28 wk	14.5	45	120	31.0	(5–10)	—	275
32 wk	15.0	47	118	32.0	(3–10)	—	290
Term^§ (cord)	16.5 (13.5)	51 (42)	108 (98)	33.0 (30.0)	(3–7)	18.1 (9–30)^\|\|	290
1–3 day	18.5 (14.5)	56 (45)	108 (95)	33.0 (29.0)	(1.8–4.6)	18.9 (9.4–34)	192
2 wk	16.6 (13.4)	53 (41)	105 (88)	31.4 (28.1)	—	11.4 (5–20)	252
1 mo	13.9 (10.7)	44 (33)	101 (91)	31.8 (28.1)	(0.1–1.7)	10.8 (4–19.5)	—
2 mo	11.2 (9.4)	35 (28)	95 (84)	31.8 (28.3)	—	—	—
6 mo	12.6 (11.1)	36 (31)	76 (68)	35.0 (32.7)	(0.7–2.3)	11.9 (6–17.5)	—
6 mo–2 yr	12.0 (10.5)	36 (33)	78 (70)	33.0 (30.0)	—	10.6 (6–17)	(150–350)
2–6 yr	12.5 (11.5)	37 (34)	81 (75)	34.0 (31.0)	(0.5–1.0)	8.5 (5–15.5)	(150–350)
6–12 yr	13.5 (11.5)	40 (35)	86 (77)	34.0 (31.0)	(0.5–1.0)	8.1 (4.5–13.5)	(150–350)
12–18 yr
Male	14.5 (13)	43 (36)	88 (78)	34.0 (31.0)	(0.5–1.0)	7.8 (4.5–13.5)	(150–350)
Female	14.0 (12)	41 (37)	90 (78)	34.0 (31.0)	(0.5–1.0)	7.8 (4.5–13.5)	(150–350)
ADULT
Male	15.5 (13.5)	47 (41)	90 (80)	34.0 (31.0)	(0.8–2.5)	7.4 (4.5–11)	(150–350)
Female	14.0 (12)	41 (36)	90 (80)	34.0 (31.0)	(0.8–4.1)	7.4 (4.5–11)	(150–350)

Hb, Hemoglobin; HCT, hematocrit; MCHC, mean cell hemoglobin concentration; MCV, mean corpuscular volume; RBC, red blood cell; WBC, white blood cell.

∗ Data are mean (− 2 SD).

† Data are mean (± 2 SD).

‡ Values are from fetal samplings.

§ 1 mo, capillary hemoglobin exceeds venous: 1 hr: 3.6 -g difference; 5 day: 2.2 -g difference; 3 wk: 1.1- g difference.

|| Mean (95% confidence limits).

Data from Forestier F, Dattos F, Galacteros F, et al. Hematologic values of 163 normal fetuses between 18 and 30 weeks of gestation. Pediatr Res. 1986;20:342; Oski FA, Naiman JL. Hematological Problems in the Newborn Infant. Philadelphia: WB Saunders;1982; Nathan D, Oski FA. Hematology of Infancy and Childhood. Philadelphia: WB Saunders; 1998; Matoth Y, Zaizor K, Varsano I, et al. Postnatal changes in some red cell parameters. Acta Paediatr Scand. 1971;60:317; and Wintrobe MM. Clinical Hematology. Baltimore: Williams & Wilkins; 1999.

2. Hemolytic anemia: Rapid RBC turnover. Etiologies: Congenital membranopathies, hemoglobinopathies, enzymopathies, metabolic defects, and immune-mediated destruction. Useful studies include:

a. Reticulocyte count: Usually elevated; indicates increased production of RBCs to compensate for increased destruction. Corrected reticulocyte count (CRC) accounts for differences in HCT and is an indicator of erythropoietic activity. CRC >1.5 suggests increased RBC production secondary to hemolysis or blood loss.

CRC=%Reticulocytes×Patient HCT/Normal HCT

b. Plasma aspartate aminotransferase (AST) and lactate dehydrogenase (LDH): Increased from release of intracellular enzymes. Serum LDH levels are significantly elevated in intravascular hemolysis and mildly elevated in extravascular hemolysis.

c. Haptoglobin: Binds free Hb; decreased with intravascular and extravascular hemolysis. Can also be decreased in patients with liver dysfunction secondary to decreased hepatic synthesis and in neonates.

d. Direct Coombs test: Tests for presence of antibody or complement on patient RBCs. May be falsely negative if affected cells have already been destroyed or antibody titer is low.

e. Indirect Coombs test: Tests for free autoantibody in patient’s serum after RBC antibody binding sites are saturated. Positive indirect test with negative direct test is typical of alloimmune sensitization (e.g., transfusion reaction).

TABLE 14-2

Classification of Anemia

Reticulocyte Count	Microcytic Anemia	Normocytic Anemia	Macrocytic Anemia
Low	Iron deficiency Lead poisoning Chronic disease Aluminum toxicity Copper deficiency Protein malnutrition	Chronic disease RBC aplasia (TEC, infection, drug induced) Malignancy Juvenile rheumatoid arthritis Endocrinopathies Renal failure	Folate deficiency Vitamin B₁₂ deficiency Aplastic anemia Congenital bone marrow dysfunction (Diamond-Blackfan or Fanconi syndromes) Drug-induced Trisomy 21 Hypothyroidism
Normal	Thalassemia trait Sideroblastic anemia	Acute bleeding Hypersplenism Dyserythropoietic anemia II	—
High	Thalassemia syndromes Hemoglobin C disorders	Antibody-mediated hemolysis Hypersplenism Microangiopathy (HUS, TTP, DIC, Kasabach-Merritt) Membranopathies (spherocytosis, elliptocytosis) Enzyme disorders (G6PD, pyruvate kinase) Hemoglobinopathies	Dyserythropoietic anemia I, III Active hemolysis

DIC, Disseminated intravascular coagulation; G6PD, glucose-6–phosphate dehydrogenase; HUS, hemolytic-uremic syndrome; RBC, red blood cell; TEC, transient erythroblastopenia of childhood; TTP, thrombotic thrombocytopenic purpura.

f. Osmotic fragility test: Useful in diagnosis of hereditary spherocytosis. Can also be positive in ABO incompatibility, autoimmune hemolytic anemia, or anytime spherocytes are present.

g. Glucose-6–phosphate dehydrogenase (G6PD) assay: Quantitative test to diagnose G6PD deficiency, an X-linked disorder affecting 10%–14% of African American males. May be normal immediately after a hemolytic episode because older, more enzyme-deficient cells have been lysed. For a comprehensive list of oxidizing drugs, go to:http://g6pddeficiency.org/index.php?cmd=contraindicated.

h. Heinz body preparation: detects precipitated Hb within RBCs; present in unstable hemoglobinopathies and enzymopathies during oxidative stress (e.g., G6PD deficiency).

3. Red cell aplasia: variable cell size, low reticulocyte count, variable platelet and white blood cell (WBC) counts. Bone marrow aspiration evaluates RBC precursors in the marrow to look for marrow dysfunction, neoplasm, or specific signs of infection.

a. Acquired aplasias:

(1) Infectious causes: parvovirus in children with rapid RBC turnover (infects RBC precursors), Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus type 6, or human immunodeficiency virus (HIV).

(2) Transient erythroblastopenia of childhood (TEC): Occurs from age 6 months to 4 years, with >80% of cases presenting after age 1 year with a normal or slightly low MCV and low reticulocyte count. Spontaneous recovery usually occurs within 4–8 weeks.

(3) Exposures include radiation and various drugs and chemicals.

b. Congenital aplasias: Typically macrocytic anemias

(1) Fanconi anemia: Autosomal recessive disorder, usually presents before 10 years of age; may present with pancytopenia. Patients may have thumb abnormalities, renal anomalies, microcephaly, or short stature. Chromosomal fragility studies can be diagnostic.

(2) Diamond-Blackfan anemia: Autosomal recessive pure RBC aplasia; presents in the first year of life. Associated with congenital anomalies in 30%-47%¹² of cases, including triphalangeal thumb, short stature, and cleft lip.

c. Aplastic anemia: Idiopathic bone marrow failure, usually macrocytic.

4. Physiologic anemia of infancy (physiologic nadir): Decrease in Hb until oxygen needs exceed oxygen delivery, usually at Hb of 9–11 mg/dL. Normally occurs at age 8–12 weeks for full-term infants and age 3–6 weeks for preterm infants.

5. Anemia of chronic inflammation: usually normocytic with normal to low reticulocyte count. Iron studies reveal low iron, TIBC, and transferrin and elevated ferritin.

II. Hemoglobinopathies

A. Hemoglobin Electrophoresis

Involves separation of Hb variants based on molecular charge and size. All positive sickle preparations and solubility tests for sickle Hb (e.g., Sickledex) should be confirmed with electrophoresis or isoelectric focusing (component of mandatory newborn screeningin many states). Table 14-3 outlines neonatal Hb electrophoresis patterns.

B. Sickle Cell Anemia

Caused by a genetic defect in β-globin; 8% of African Americans are carriers; 1 in 500 African Americans have sickle cell anemia.

1. Diagnosis: Often made on newborn screen with Hb electrophoresis. The sickle preparation and Sickledex are rapid tests that are positive in all sickle hemoglobinopathies. False-negative test results may be seen in neonates and other patients with a high percentage of fetal Hb.

2. Complications (Table 14-4): A hematologist should be consulted.

3. Health maintenance^1,2: Ongoing consultation and clinical involvement with a pediatric hematologist and/or sickle cell program are essential (Table 14-5).

4. Hemoglobin electrophoresis (outside neonatal period): hemoglobin SF, SCF, SAF—other Hb combinations may sickle.

TABLE 14-3

Neonatal Hemoglobin (Hb) Electrophoresis Patterns ^∗

FA	Fetal Hb and adult normal Hb; the normal newborn pattern
FAV	Indicates presence of both HbF and HbA, but an anomalous band (V) is present that does not appear to be any of the common Hb variants.
FAS	Indicates fetal Hb, adult normal HbA, and HbS, consistent with benign sickle cell trait
FS	Fetal and sickle HbS without detectable adult normal HbA. Consistent with clinically significant homozygous sickle Hb genotype (S/S) or sickle β-thalassemia, with manifestations of sickle cell anemia during childhood.
FC^†	Designates presence of HbC without adult normal HbA. Consistent with clinically significant homozygous HbC genotype (C/C), resulting in a mild hematologic disorder presenting during childhood.
FSC	HbS and HbC present. This heterozygous condition could lead to manifestations of sickle cell disease during childhood.
FAC	HbC and adult normal HbA present, consistent with benign HbC trait
FSA	Heterozygous HbS/β-thalassemia, a clinically significant sickling disorder
F^†	Fetal HbF is present without adult normal HbA. May indicate delayed appearance of HbA but is also consistent with homozygous β-thalassemia major or homozygous hereditary persistence of fetal HbF.
FV^†	Fetal HbF and an anomalous Hb variant (V) are present.
AF	May indicate prior blood transfusion. Submit another filter paper blood specimen when infant is 4 mo of age, at which time the transfused blood cells should have been cleared.

NOTE: HbA: α₂β₂; HbF: α₂γ₂; HbA₂: α₂δ₂.

∗ Hemoglobin variants are reported in order of decreasing abundance; for example, FA indicates more fetal than adult hemoglobin.

† Repeat blood specimen should be submitted to confirm original interpretation.

C. Thalassemias

Defects in α- or β-globin production. The predominant adult hemoglobin is HbA (α₂β₂), a tetramer composed of two α and two β chains. The α-Globin production is dependent on four genes, and β-globin production is dependent on two genes. Imbalance in production of globin chains leads to precipitation of excess chains, causing ineffective erythropoiesis and shortened survival of mature RBCs.

1. α-Thalassemias:

a. Silent carriers (α−/αα): not anemic, childhood and adult hemoglobin electrophoresis usually normal.

TABLE 14-4

Sickle Cell Disease Complications

Complication	Evaluation	Treatment
Fever (T ≥38.5°C)	History and physical CBC with differential Reticulocyte count Blood cultures Chest x-ray Other cultures as indicated	IV antibiotics (third-generation cephalosporin, other antibiotics as indicated, especially if penicillin-resistant pneumococcus suspected) Admit if ill appearing, <3 yr of age, concerning lab results, or complications. Some centers use antibiotics with a long half-life and reevaluate in 24 hr as an outpatient.
Vaso-occlusive crisis Children <2 yr, dactylitis Children >2 yr, unifocal or multifocal pain	History and physical CBC with differential Reticulocyte count Type and screen	Oral analgesics as an outpatient, as tolerated IV analgesics and IV fluids if outpatient therapy fails (parenteral narcotics in form of PCA and parenteral NSAIDs, usually in combination) Aggressive early treatment of pain is essential.
Acute chest syndrome New pulmonary infiltrate with fever, cough, chest pain, tachypnea, dyspnea, or hypoxia	History and physical CBC with differential Reticulocyte count Blood cultures Chest x-ray Type and screen	Admit O₂, incentive spirometry, bronchodilators IV antibiotics (third-generation cephalosporin and macrolide) Analgesia, IV fluids Simple transfusion or partial exchange for moderately severe illness; double the packed cell volume exchange transfusion for severe or rapidly progressing illness. High-dose dexamethasone controversial (risk of readmission for pain or other SCD-related issues)⁷
Splenic sequestration Acutely enlarged spleen and Hb level ≥2 g/dL below patient’s baseline	History and physical CBC Reticulocyte count Type and hold	Serial abdominal exams IV fluids and fluid resuscitation as necessary RBC transfusion or, in severe cases, exchange transfusion for cardiovascular compromise and Hb <4.5 g/dL. (Autotransfusion may occur with recovery, leading to increased Hb and CHF. Transfuse cautiously.)
Table Continued

Complication	Evaluation	Treatment
Aplastic crisis Acute illness with Hb below patient’s baseline and low reticulocyte count May follow viral illnesses, especially parvovirus B19	History and physical CBC with differential Reticulocyte count Type and screen Parvovirus serology and polymerase chain reaction	Admit IV fluids PRBCs for symptomatic anemia Isolation to protect susceptible individuals and women of childbearing age until parvovirus excluded
Other complications Priapism, CVA, TIA, gallbladder disease, avascular necrosis, hyphema ^∗

NOTE: CVA requires emergency transfusion guided by a hematologist and a neurologist experienced with sickle cell disease. Exchange transfusion preferable to simple transfusion if possible.⁸
Abbreviations: CBC, Complete blood cell count; CHF, congestive heart failure; CVA, cerebrovascular accident; Hb, hemoglobin; IV, intravenous; NSAIDs, nonsteroidal anti-inflammatory drugs; PCA, patient-controlled analgesia; PRBCs, packed red blood cells; RBC, red blood cells; SCD, sickle cell disease; T, temperature; TIA, transient ischemic attack.

^∗ Hyphema in a patient with sickle cell trait is an ophthalmologic emergency

TABLE 14-5

Sickle Cell Disease Health Maintenance

Immunizations	Maintenance
Pneumococcal vaccine	Vaccinate with 13-valent conjugate vaccine as per routine childhood schedule, 23-valent polysaccharide vaccine at age 2, booster at age 5.
Meningococcal vaccine	Give at age 2 and every 5 yr thereafter.
Influenza vaccine	Vaccinate yearly beginning at age 6 mo.
MEDICATIONS
PCN	Begin as soon as SCD diagnosis made (125 mg BID; increase dose to 250 mg BID at age 3^∗).
Folic acid	Consider supplementation, start by age 1.
Hydroxyurea	Consider with frequent crises or in severe disease.^†
IMAGING
Transcranial Doppler (TCD)	Perform annually from ages 2 to 16 to evaluate for increased risk of cerebrovascular accident (CVA).
OTHER
Ophthalmology	Perform annually from age 10 to evaluate for sickle retinopathy.
Growth and development, school/social issues, counseling regarding fevers	Review closely at all visits.

PCN, Penicillin; SCD, sickle cell disease.

∗ Prophylaxis may be discontinued by age 5 if patient has had no prior severe pneumococcal infections or splenectomy and has documented pneumococcal vaccinations, including second 23-valent vaccination. Practice patterns vary. Some continue penicillin indefinitely.

† Increases levels of fetal Hb and decreases HbS polymerization in cells. Has been shown to significantly decrease episodes of vaso-occlusive crises, dactylitis, acute chest syndrome, number of transfusions, and hospitalizations.9,13 May decrease mortality in adults.

b. α-Thalassemia trait (α−/α−) or (αα/−): Causes mild microcytic anemia, childhood and adult hemoglobin electrophoresis usually normal. Hb Barts can be seen in infancy (e.g., on state newborn screens) in patients with α-thalassemia trait.

c. HbH disease (β₄) (α−/−−): Causes moderately severe anemia.

d. Hb Bart/hydrops fetalis (−−/−−): Hb Bart (γ₄) cannot deliver oxygen; usually fatal.

2. β-Thalassemia: Found throughout the Mediterranean, Middle East, India, and Southeast Asia. Ineffective erythropoiesis is more severe in β-thalassemia than α-thalassemia because excess α chains are more unstable than β chains. Adult hemoglobin electrophoresis with decreased hemoglobin A, increased hemoglobin A₂, and increased hemoglobin F.

a. Thalassemia trait/thalassemia minor (β/β+) or (β/β0): Usually asymptomatic, with microcytosis out of proportion to anemia, sometimes with erythrocytosis.

b. Thalassemia intermedia (β+/β+): Presents at about age 2 years with moderate compensated anemia that may become symptomatic, leading to heart failure, pulmonary hypertension, splenomegaly, and bony expansion, usually in second or third decade of life.

c. Thalassemia major/Cooley’s anemia (β0/β0, β+/β0, or β+/β+): Presence of anemia within first 6 months of life, with hepatosplenomegaly and progressive bone marrow expansion that may lead to frontal bossing, maxillary hyperplasia, and other skeletal deformities. Regular transfusions required to avoid anemia.

III. Neutropenia

An absolute neutrophil count (ANC) <1500/µL, although neutrophil counts vary with age (Table 14-6). Severe neutropenia is defined as an ANC <500/µL. Children with significant neutropenia are at risk for bacterial and fungal infections. Granulocyte colony-stimulating factor may be indicated. Transient neutropenia secondary to viral illness rarely causes significant morbidity. Autoimmune neutropenia is a common cause of neutropenia in children 6 mo–6 yr. Testing for antineutrophil antibodies is indicated in this age group and may obviate the need for more extensive workup. For management of fever and neutropenia in oncology patients, see Chapter 22, Figure 22-1. Box 14-1 lists causes.

IV. Thrombocytopenia

A. Definition

Platelet count <150,000/µL. Clinically significant bleeding is unlikely with platelet counts >20,000/µL in the absence of other complicating factors.

B. Causes of Thrombocytopenia

1. Idiopathic thrombocytopenic purpura (ITP): A diagnosis of exclusion; can be acute or chronic. WBC count, Hb levels, and peripheral blood smear are normal. Many require no therapy, and indications for treatment of patients without significant bleeding are not well established.

a. Treatment options:

(1) Intravenous immune globulin (see Formulary for IVIG dosing)

(2) Corticosteroids (i.e., prednisone 2 mg/kg/day or up to 30 mg/kg methylprednisolone for up to 3 days)

(3) Anti-Rh (D) immune globulin (WinRho). Useful only in Rh-positive nonsplenectomized patients. Should not be used in patients with preexisting hemolysis or renal disease; monitor for signs of intravascular hemolysis after administration. Disseminated intravascular coagulation (DIC) has been reported. See package insert for blackbox warning and monitoring guidelines.

(4) Consider rituximab in chronic cases.³

(5) Splenectomy or chemotherapy may be considered in chronic cases. Platelet transfusions are not generally helpful but necessary in life-threatening bleeding.

TABLE 14-6

Age-Specific Leukocyte Differential

Age	Total Leukocytes^∗	Neutrophils^†		Lymphocytes		Monocytes		Eosinophils
Age	Mean (range)	Mean (range)	%	Mean (range)	%	Mean	%	Mean	%
Birth	18.1 (9–30)	11 (6–26)	61	5.5 (2–11)	31	1.1	6	0.4	2
12 hr	22.8 (13–38)	15.5 (6–28)	68	5.5 (2–11)	24	1.2	5	0.5	2
24 hr	18.9 (9.4–34)	11.5 (5–21)	61	5.8 (2–11.5)	31	1.1	6	0.5	2
1 wk	12.2 (5–21)	5.5 (1.5–10)	45	5.0 (2–17)	41	1.1	9	0.5	4
2 wk	11.4 (5–20)	4.5 (1–9.5)	40	5.5 (2–17)	48	1.0	9	0.4	3
1 mo	10.8 (5–19.5)	3.8 (1–8.5)	35	6.0 (2.5–16.5)	56	0.7	7	0.3	3
6 mo	11.9 (6–17.5)	3.8 (1–8.5)	32	7.3 (4–13.5)	61	0.6	5	0.3	3
1 yr	11.4 (6–17.5)	3.5 (1.5–8.5)	31	7.0 (4–10.5)	61	0.6	5	0.3	3
2 yr	10.6 (6–17)	3.5 (1.5–8.5)	33	6.3 (3–9.5)	59	0.5	5	0.3	3
4 yr	9.1 (5.5–15.5)	3.8 (1.5–8.5)	42	4.5 (2–8)	50	0.5	5	0.3	3
6 yr	8.5 (5–14.5)	4.3 (1.5–8)	51	3.5 (1.5–7)	42	0.4	5	0.2	3
8 yr	8.3 (4.5–13.5)	4.4 (1.5–8)	53	3.3 (1.5–6.8)	39	0.4	4	0.2	2
10 yr	8.1 (4.5–13.5)	4.4 (1.5–8.5)	54	3.1 (1.5–6.5)	38	0.4	4	0.2	2
16 yr	7.8 (4.5–13.0)	4.4 (1.8–8)	57	2.8 (1.2–5.2)	35	0.4	5	0.2	3
21 yr	7.4 (4.5–11.0)	4.4 (1.8–7.7)	59	2.5 (1–4.8)	34	0.3	4	0.2	3

∗ Numbers of leukocytes are × 10³/µL; ranges are estimates of 95% confidence limits; percents refer to differential counts.

† Neutrophils include band cells at all ages and a small number of metamyelocytes and myelocytes in the first few days of life.

Adapted from Cairo MS, Brauho F. Blood and blood-forming tissues. In: Randolph AM, ed. Pediatrics. 21st ed. New York: McGraw-Hill, 2003.

BOX 14-1 DIFFERENTIAL DIAGNOSIS OF CHILDHOOD NEUTROPENIA

Acquired	Congenital
Infection Immune-mediated Chronic benign neutropenia of childhood Hypersplenism Vitamin B₁₂, folate, copper deficiency Drugs or toxic substances Aplastic anemia Malignancies or preleukemic disorders Ionizing radiation	Cyclic neutropenia Severe congenital neutropenia (e.g., Kostmann syndrome) Shwachman-Diamond syndrome Fanconi anemia Metabolic disorders (e.g., amino acidopathies, Barth syndrome, glycogen storage disorders) Osteopetrosis Neutropenia with pigmentation abnormalities (e.g., Chédiak-Higashi anomaly)

2. Neonatal thrombocytopenia: May be caused by:

a. Decreased production: Results from aplastic disorders, congenital malignancy such as leukemia, and viral infections

b. Increased consumption: Usually result of DIC due to infection or asphyxia.

c. Immune mediated: Immunoglobulin (Ig)G or complement attach to platelets and cause destruction. Specific causes include preeclampsia, sepsis, maternal ITP, and platelet alloimmunization.

3. Neonatal alloimmune thrombocytopenia (NAIT): Transplacental maternal antibodies (usually against PLA-1 antigen/HPA-1a) cause fetal platelet destruction. If severe, a transfusion of maternal platelets will be more effective than random donor platelets in raising infant’s platelet count.

a. Evaluation/diagnosis:

(1) Check maternal platelet count and platelet-associated IgG. Mother’s platelet count should be normal and platelet-associated IgG usually negative.

(2) Absence of maternal PLA-1 antigen/HPA-1a or other specific antigens

(3) Study of mother’s or infant’s plasma with a panel of known minor platelet antigens

(4) Mixing study of maternal or neonatal plasma and paternal platelets.

4. Causes of microangiopathic hemolytic anemia: DIC, hemolytic-uremic syndrome/thrombotic thrombocytopenic purpura (HUS/TTP)

a. HUS/TTP: Characterized by the triad of microangiopathic hemolytic anemia, uremia, and thrombocytopenia. HUS is often triggered by bacterial enteritis, especially caused by Escherichia coli O157:H7, although there are a variety of causes. HUS does not typically include coagulation abnormalities like those seen in DIC. Avoid blood products in patients with HUS thought to be secondary to pneumococcal infection. TTP includes the triad of HUS in addition to fever and central nervous system (CNS) changes and is more common in older adolescents and adults.

b. DIC (see Box 14-5)

5. Other causes of thrombocytopenia: Infection causing marrow suppression, malignancy, HIV, drug-induced thrombocytopenia, marrow infiltration, cavernous hemangiomas (Kasabach-Merritt syndrome), thrombocytopenia with absent radii syndrome (TAR), thrombosis, hypersplenism, and other rare inherited disorders (e.g., Wiskott-Aldrich, Paris-Trousseau, Noonan, and DiGeorge syndromes; myosin 9– associated megaplatelet disorders; chromosomal abnormalities).

V. Coagulation (Fig. 14-2)

A. Tests of Coagulation

An incorrect anticoagulant-to-blood ratio will give inaccurate results. Table 14-7 lists normal hematologic values for coagulation testing.

1. Activated partial thromboplastin time (aPTT): Measures intrinsic system; requires factors V, VIII, IX, X, XI, XII, fibrinogen, and prothrombin. May be prolonged in heparin administration, hemophilia, von Willebrand disease (v WD), DIC, and in the presence of circulating inhibitors (e.g., lupus anticoagulants).

2. Prothrombin time (PT): Measures extrinsic pathway; requires factors V, VII, X, fibrinogen, and prothrombin. May be prolonged in warfarin administration, deficiencies of vitamin K–associated factors, malabsorption, liver disease, DIC, and the presence of circulating inhibitors.

FIGURE 14-2 Coagulation cascade. AT, Antithrombin; F, factor; HMWK, high-molecular-weight kininogen; PL, phospholipid; TF, tissue factor; TFPI, tissue factor pathway inhibitor. (Adaptation courtesy James Casella and Clifford Takemoto.)

TABLE 14-7

Age-Specific Coagulation Values

Coagulation Test	Preterm Infant (30–36 wk), Day of Life 1^∗	Term Infant, Day of Life 1	Day of Life 3	1 Month–1 yr	1–5 yr	6–10 yr	11–16 yr	Adult
PT (sec)	13.0 (10.6–16.2)	15.6 (14.4–16.4)	14.9 (13.5–16.4)	13.1 (11.5–15.3)	13.3 (12.1–14.5)	13.4 (11.7–15.1)	13.8 (12.7–16.1)	13.0 (11.5–14.5)
INR		1.26 (1.15–1.35)	1.20 (1.05–1.35)	1.00 (0.86–1.22)	1.03 (0.92–1.14)	1.04 (0.87–1.20)	1.08 (0.97–1.30)	1.00 (0.80–1.20)
aPTT (sec)^†	53.6 (27.5–79.4)	38.7 (34.3–44.8)	36.3 (29.5–42.2)	39.3 (35.1–46.3)	37.7 (33.6–43.8)	37.3 (31.8–43.7)	39.5 (33.9–46.1)	33.2 (28.6–38.2)
Fibrinogen (g/L)	2.43 (1.50–3.73)	2.80 (1.92–3.74)	3.30 (2.83–4.01)	2.42 (0.82–3.83)	2.82 (1.62–4.01)	3.04 (1.99–4.09)	3.15 (2.12–4.33)	3.1 (1.9–4.3)
Bleeding time (min)^∗					6 (2.5–10)	7 (2.5–13)	5 (3–8)	4 (1–7)
Thrombin time (sec)	14 (11–17)	12 (10–16)^∗		17.1 (16.3–17.6)	17.5 (16.5–18.2)	17.1 (16.1–18.5)	16.9 (16.2–17.6)	16.6 (16.2–17.2)
Factor II (U/mL)	0.45 (0.20–0.77)	0.54 (0.41–0.69)	0.62 (0.50–0.73)	0.90 (0.62–1.03)	0.89 (0.70–1.09)	0.89 (0.67–1.10)	0.90 (0.61–1.07)	1.10 (0.78–1.38)
Factor V (U/mL)	0.88 (0.41–1.44)	0.81 (0.64–1.03)	1.22 (0.92–1.54)	1.13 (0.94–1.41)	0.97 (0.67–1.27)	0.99 (0.56–1.41)	0.89 (0.67–1.41)	1.18 (0.78–1.52)
Factor VII (U/mL)	0.67 (0.21–1.13)	0.70 (0.52–0.88)	0.86 (0.67–1.07)	1.28 (0.83–1.60)	1.11 (0.72–1.50)	1.13 (0.70–1.56)	1.18 (0.69–2.00)	1.29 (0.61–1.99)
Factor VIII (U/mL)	1.11 (0.50–2.13)	1.82 (1.05–3.29)	1.59 (0.83–2.74)	0.94 (0.54–1.45)	1.10 (0.36–1.85)	1.17 (0.52–1.82)	1.20 (0.59–2.00)	1.60 (0.52–2.90)
vWF (U/mL)^∗	1.36 (0.78–2.10)	1.53 (0.50–2.87)			0.82 (0.47–1.04)	0.95 (0.44–1.44)	1.00 (0.46–1.53)	0.92 (0.5–1.58)
Factor IX (U/mL)	0.35 (0.19–0.65)	0.48 (0.35–0.56)	0.72 (0.44–0.97)	0.71 (0.43–1.21)	0.85 (0.44–1.27)	0.96 (0.48–1.45)	1.11 (0.64–2.16)	1.30 (0.59–2.54)
Factor X (U/mL)	0.41 (0.11–0.71)	0.55 (0.46–0.67)	0.60 (0.46–0.75)	0.95 (0.77–1.22)	0.98 (0.72–1.25)	0.97 (0.68–1.25)	0.91 (0.53–1.22)	1.24 (0.96–1.71)
Factor XI (U/mL)	0.30 (0.08–0.52)	0.30 (0.07–0.41)	0.57 (0.24–0.79)	0.89 (0.62–1.25)	1.13 (0.65–1.62)	1.13 (0.65–1.62)	1.11 (0.65–1.39)	1.12 (0.67–1.96)
Factor XII (U/mL)	0.38 (0.10–0.66)	0.58 (0.43–0.80)	0.53 (0.14–0.80)	0.79 (0.20–1.35)	0.85 (0.36–1.35)	0.81 (0.26–1.37)	0.75 (0.14–1.17)	1.15 (0.35–2.07)
PK (U/mL)^∗	0.33 (0.09–0.57)	0.37 (0.18–0.69)			0.95 (0.65–1.30)	0.99 (0.66–1.31)	0.99 (0.53–1.45)	1.12 (0.62–1.62)
HMWK (U/mL)^∗	0.49 (0.09–0.89)	0.54 (0.06–1.02)			0.98 (0.64–1.32)	0.93 (0.60–1.30)	0.91 (0.63–1.19)	0.92 (0.50–1.36)
Factor XIIIa (U/mL)^∗	0.70 (0.32–1.08)	0.79 (0.27–1.31)			1.08 (0.72–1.43)	1.09 (0.65–1.51)	0.99 (0.57–1.40)	1.05 (0.55–1.55)
Factor XIIIs (U/mL)^∗	0.81 (0.35–1.27)	0.76 (0.30–1.22)			1.13 (0.69–1.56)	1.16 (0.77–1.54)	1.02 (0.60–1.43)	0.97 (0.57–1.37)
d-Dimer		1.47 (0.41–2.47)	1.34 (0.58–2.74)	0.22 (0.11–0.42)	0.25 (0.09–0.53)	0.26 (0.10–0.56)	0.27 (0.16–0.39)	0.18 (0.05–0.42)
FDPs^∗								Borderline titer = 1:25–1:50 Positive titer <1:50
Table Continued

Coagulation Test	Preterm Infant (30–36 wk), Day of Life 1^∗	Term Infant, Day of Life 1	Day of Life 3	1 Month–1 yr	1–5 yr	6–10 yr	11–16 yr	Adult
COAGULATION INHIBITORS
ATIII (U/mL)^∗	0.38 (0.14–0.62)	0.63 (0.39–0.97)			1.11 (0.82–1.39)	1.11 (0.90–1.31)	1.05 (0.77–1.32)	1.0 (0.74–1.26)
α₂-M (U/mL)^∗	1.10 (0.56–1.82)	1.39 (0.95–1.83)			1.69 (1.14–2.23)	1.69 (1.28–2.09)	1.56 (0.98–2.12)	0.86 (0.52–1.20)
C1-Inh (U/mL)^∗	0.65 (0.31–0.99)	0.72 (0.36–1.08)			1.35 (0.85–1.83)	1.14 (0.88–1.54)	1.03 (0.68–1.50)	1.0 (0.71–1.31)
α₂-AT (U/mL)^∗	0.90 (0.36–1.44)	0.93 (0.49–1.37)			0.93 (0.39–1.47)	1.00 (0.69–1.30)	1.01 (0.65–1.37)	0.93 (0.55–1.30)
Protein C (U/mL)	0.28 (0.12–0.44)	0.32 (0.24–0.40)	0.33 (0.24–0.51)	0.77 (0.28–1.24)	0.94 (0.50–1.34)	0.94 (0.64–1.25)	0.88 (0.59–1.12)	1.03 (0.54–1.66)
Protein S (U/mL)	0.26 (0.14–0.38)	0.36 (0.28–0.47)	0.49 (0.33–0.67)	1.02 (0.29–1.62)	1.01 (0.67–1.36)	1.09 (0.64–1.54)	1.03 (0.65–1.40)	0.75 (0.54–1.03)
FIBRINOLYTIC SYSTEM^∗
Plasminogen (U/mL)	1.70 (1.12–2.48)	1.95 (1.60–2.30)			0.98 (0.78–1.18)	0.92 (0.75–1.08)	0.86 (0.68–1.03)	0.99 (0.7–1.22)
TPA (ng/mL)					2.15 (1.0–4.5)	2.42 (1.0–5.0)	2.16 (1.0–4.0)	4.90 (1.40–8.40)
α₂-AP (U/mL)	0.78 (0.4–1.16)	0.85 (0.70–1.0)			1.05 (0.93–1.17)	0.99 (0.89–1.10)	0.98 (0.78–1.18)	1.02 (0.68–1.36)
PAI (U/mL)					5.42 (1.0–10.0)	6.79 (2.0–12.0)	6.07 (2.0–10.0)	3.60 (0–11.0)

α₂-AP, α₂-Antiplasmin; α₂-AT, α₂-antitrypsin; α₂-M, α₂-macroglobulin; aPTT, activated partial thromboplastin time; ATIII, antithrombin III; FDPs, fibrin degradation products; HMWK, high-molecular-weight kininogen; INR, international normalized ratio; PAI, plasminogen activator inhibitor; PK, prekallikrein; PT, prothrombin time; TPA, tissue plasminogen activator; VIII, factor VIII procoagulant; vWF, von Willebrand factor.

∗ Data from Andrew M, Paes B, Milner R, et al. Development of the human anticoagulant system in the healthy premature infant. Blood. 1987;70:165-172; Andrew M, Paes B, Milner R, et al. Development of the human anticoagulant system in the healthy premature infant. Blood. 1988;72:1651-1657; and Andrew M, Vegh P, Johnston M, et al. Maturation of the hemostatic system during childhood. Blood. 1992;8:1998-2005.

† aPTT values may vary depending on reagent.

Adapted from Monagle P, Barnes C, Ignjatovic, V, et al. Developmental haemostasis. Impact for clinical haemostasis laboratories. Thromb Haemost. 2006;95;362-372.

3. Platelet function testing: Platelet aggregation and the Platelet Function Analyzer-100 (PFA-100) system are in vitro methods for measuring platelet function. Bleeding time (BT) evaluates clot formation, including platelet number and function and von Willebrand factor (vWF). Always assess the platelet number and history of ingestion of platelet inhibitors (e.g., nonsteroidal antiinflammatory drugs [NSAIDs]) before any platelet function testing.

B. Hypercoagulable States

Present clinically as venous or arterial thrombosis (Box 14-2)

1. Laboratory evaluation^4,5:

a. Initial laboratory screening includes PT and high-sensitivity aPTT; if PT or aPTT are prolonged, a mixing study to look for circulating anticoagulants.

b. Extended workup for hypercoagulable states (Box 14-3): A hematologist should be consulted.

BOX 14-2 HYPERCOAGULABLE CONDITIONS

Congenital	Acquired
Protein C and S deficiency: Hereditary autosomal dominant disorder. Heterozygotes have three- to sixfold increased risk for venous thrombosis. Antithrombin III deficiency: Hereditary autosomal dominant disorder. Homozygotes die in infancy. Factor V Leiden (activated protein C resistance): 2%–5% of European whites are heterozygotes with two- to four-fold increased risk for venous thrombosis; 1 in 1000 are homozygotes, with 80- to 100-fold increased risk for venous thrombosis. Homocystinemia: Increased levels of homocysteine associated with arterial and venous thromboses, often due to MTHFR abnormalities Others: Prothrombin mutation (G20210A), plasminogen abnormalities, fibrinogen abnormalities	Endothelial damage: Causes include vascular catheters, smoking, diabetes, hypertension, surgery, hyperlipidemia. Hyperviscosity: Macroglobulinemia, polycythemia, sickle cell disease Antiphospholipid antibodies: Seen in patients with systemic lupus erythematosus or other autoimmune diseases; can occur with infections or idiopathically. Associated with venous and arterial thromboses and spontaneous abortions. Platelet activation: Caused by essential thrombocytosis, oral contraceptives, heparin-induced thrombocytopenia Others: Drugs, malignancy, liver disease, inflammatory disease such as inflammatory bowel disease, paroxysmal nocturnal hemoglobinuria, lipoprotein A

Congenital

Acquired

Protein C and S deficiency: Hereditary autosomal dominant disorder. Heterozygotes have three- to sixfold increased risk for venous thrombosis.

Antithrombin III deficiency: Hereditary autosomal dominant disorder. Homozygotes die in infancy.

Factor V Leiden (activated protein C resistance): 2%–5% of European whites are heterozygotes with two- to four-fold increased risk for venous thrombosis; 1 in 1000 are homozygotes, with 80- to 100-fold increased risk for venous thrombosis.

Homocystinemia: Increased levels of homocysteine associated with arterial and venous thromboses, often due to MTHFR abnormalities

Others: Prothrombin mutation (G20210A), plasminogen abnormalities, fibrinogen abnormalities

Endothelial damage: Causes include vascular catheters, smoking, diabetes, hypertension, surgery, hyperlipidemia.

Hyperviscosity: Macroglobulinemia, polycythemia, sickle cell disease

Antiphospholipid antibodies: Seen in patients with systemic lupus erythematosus or other autoimmune diseases; can occur with infections or idiopathically. Associated with venous and arterial thromboses and spontaneous abortions.

Platelet activation: Caused by essential thrombocytosis, oral contraceptives, heparin-induced thrombocytopenia

Others: Drugs, malignancy, liver disease, inflammatory disease such as inflammatory bowel disease, paroxysmal nocturnal hemoglobinuria, lipoprotein A

MTHFR, Methyltetrahydrofolate reductase.

c. Identification of one risk factor (e.g., indwelling vascular catheter) does not preclude the search for others, especially when accompanied by a family or personal history of thrombosis.

2. Treatment of thromboses:

a. Unfractionated heparin (UFH): Used for treatment or prevention of deep venous thrombosis (DVT) or pulmonary embolism (PE), atrial fibrilliation, mechanical heart valve, arterial thrombosis, cerebral sinovenous thrombosis, cardioembolic arterial ischemic stroke, homozygous purpura fulminans, and for bridge to warfarin therapy

(1) See Tables 14-8 to 14-11 for UFH bolus and drip adjustment guidelines for goal heparin anti-Xa level range of 0.3–0.7 U/mL or aPTT range 50–80 seconds.

(2) UFH may be reversed with protamine.

(3) UFH or low-molecular-weight-heparin (LMWH) therapy should continue for at least 5–7 days while initiating warfarin for treatment of venous thrombosis.

Contraindications: Patients with known hypersensitivity to heparin, major active bleeding, known or suspected heparin-induced thrombocytopenia (HIT), or concurrent epidural therapy

Precautions: Patients at high risk for bleeding (general bleeding precaution protocols must be implemented) or with platelet count <50,000/mm³. Avoid intramuscular injections and avoid other drugs that affect platelet function (e.g., NSAIDs, aspirin, clopidogrel).

BOX 14-3 EXTENDED WORKUP FOR HYPERCOAGULABLE STATES ^∗

Suggested tiered testing approach:

First Tier:

Antithrombin III activity (antithrombin III deficiency and dysfunction)

Activated protein C resistance assay (screening test for factor V Leiden)

Factor V Leiden (DNA-based assay for factor V Leiden)

Factor II 20210A (prothrombin mutation)

Homocysteine

Methyltetrahydrofolate reductase (MTHFR) genetic testing if homocysteine elevated

Dilute Russell viper venom test (antiphospholipid antibody syndrome)

Anticardiolipin screening enzyme-linked immunosorbent assay (ELISA; anticardiolipin antibodies)

Protein C activity (protein C deficiency and dysfunction)

Protein S activity (protein S deficiency and dysfunction)

Factor VIII, IX, XI

Second Tier (less common conditions):

Platelet neutralization procedure (lupus anticoagulant)

Plasminogen activity

Tissue plasminogen activator (TPA) antigen

Plasminogen activator inhibitor activity (PAI-1; measures activity of this TPA inhibitor)

α₂-Antiplasmin activity (measures activity of this plasmin inhibitor)

Lipoprotein (a) (Lp[a]) promotes decreased fibrinolysis

^∗ Where necessary, abnormality tested for is listed in parentheses.

TABLE 14-8

Unfractionated Heparin Dose Initiation Guidelines for Goal aPTT Range of 50–80 Seconds ^∗

Age	Loading Dose (No Loading Dose for Stroke Patients)	Initial Infusion Rate	Monitoring Parameters
Neonates and infants <1 yr	75 units/kg intravenously (IV)	28 units/kg/hr	Obtain aPTT 4 hr after loading dose.
Children ≥1 yr–16 yr	75 units/kg IV (max dose = 7700 units)	20 units/kg/hr (initial max rate = 1650 units/hr)	Obtain aPTT 4 hr after loading dose.
Patients >16 yr	70 units/kg (max dose = 7700 units)	15 units/kg/hr (initial max rate = 1650 units/hr)	Obtain aPTT 4 hr after loading dose.

^∗ Reflects antifactor Xa level of 0.3–0.7 IU/mL with current activated partial thromboplastin time (aPTT) reagents at Johns Hopkins Hospital 2/3/11. Therapeutic aPTT range may vary with different aPTT reagents.

TABLE 14-9

Unfractionated Heparin Dose Adjustment Algorithm for Goal aPTT Range of 50–80 Seconds ^∗

aPTT (seconds)	Bolus (units/kg)	Hold (minutes)	Rate Change	Repeat aPTT (hours)
≤39	50	0	Increase 20%	4 hr
40–49	0	0	Increase 10%	4 hr
50–80	0	0	0	4 hr, then next day once two consecutive values are in range
81–100	0	0	Decrease 10%	6 hr
101–125	0	30–60 min	Decrease 20%	6 hr
≥125^†	0	60–120 min until aPTT <115 sec	Decrease 30%; restart when aPTT <115 sec	6 hr after infusion is restarted

^∗ Reflects antifactor Xa level of 0.3–0.7 IU/mL with current activated partial thromboplastin (aPTT) reagents at Johns Hopkins Hospital 2/3/11. Therapeutic aPTT range may vary with different aPTT reagents.

† Confirm that specimen was not drawn from heparinized line or same extremity as site of heparin infusion.

TABLE 14-10

Unfractionated Heparin Dose Initiation Guidelines For Goal Anti-Xa Activity of 0.3-0.7 Units/ML

Age	Loading Dose (No Bolus for Stroke Patients)	Initial Infusion Rate	Monitoring Parameters
Neonates and infants <1 year	75 units/kg IV	28 units/kg/hr	Obtain anti-Xa 4 hours after loading dose
Children ≥1 year–16 years	75 units/kg IV (max dose = 7700 units)	20 units/kg/hr (max rate = 1650 units/hour)	Obtain anti-Xa 4 hours after loading dose
Patients > 16 years	70 units/kg (max dose = 7700 units)	15 units/kg/hr (max rate = 1650 units/hr)	Obtain anti-Xa 4 hours after loading dose

TABLE 14-11

Unfractionated Heparin Dose Adjustment Algorithm For Goal Anti-Xa Activity of 0.3–0.7 Units/ML

Anti-Xa level	Bolus (units/kg)	Hold (minutes)	Rate Change	Repeat anti-Xa (hours)
≤0.1	50	0	Increase 20%	4 hr
0.2	0	0	Increase 10%	4 hr
0.3–0.7	0	0	0	4 hr, then next day once two consecutive values are in range
0.8–0.9	0	0	Decrease 10%	6 hr
1.0–1.1	0	30–60	Decrease 20%	6 hr
>1.2^∗	0	60–120 until anti-Xa <1.0	Decrease 30%; restart when anti-Xa activity <1.0	6 hr after infusion is restarted

∗ Confirm that specimen was not drawn from heparinized line or same extremity as site of heparin infusion.

Baseline labs prior to institution of UFH therapy (to assess baseline coagulation state): aPTT, PT, BMP, Heme-8.

b. LMWH 4,5: Administered subcutaneously, has a longer half-life, more predictable pharmacokinetics, and requires less monitoring. Also associated with lower risk for HIT.

(1) Dose depends on preparation. See Formulary for enoxaparin dosage information.

(2) Monitor LMWH therapy by following anti-Xa activity. Therapeutic range is 0.5–1.0 U/mL for thrombosis treatment and 0.1–0.3 U/mL for prophylactic dosing. Blood for anti-Xa activity should be drawn 4 hours after dose.

(3) LMWH-induced bleeding can be partially reversed with protamine. Consult hematologist for protamine reversal protocol.

c. Warfarin: Used for long-term anticoagulation. Patient should receive heparin (UFH or LMWH) while initiating warfarin therapy, owing to possibility of hypercoagulability from decreased protein C and S levels.

(1) Usually administered orally at an initiation dose for 1–2 days, followed by a daily dose sufficient to maintain the PT/INR in the desired range. Infants often require higher daily doses. Levels should be measured every 1–4 weeks. Table 14-12 lists dose adjustment guidelines, and Table 14-13 outlines management of excessive anticoagulation.

(2) Efficacy is greatly affected by dietary intake of vitamin K. Patients should receive appropriate dietary education.

(3) Box 14-4 lists medications that influence warfarin therapy.

d. Anticoagulant therapy alters many coagulation tests:

(1) Heparin prolongs aPTT, thrombin time, dilute Russell Viper Venom test (dRVVT), and mixing studies.

TABLE 14-12

Adjustment and Monitoring of Warfarin to Maintain an International Normalized Ratio (INR) Between 2 and 3 ^∗,¹¹

I. Day 1 Initial Dosing

1. Newborn: for age <3 mo, there are limited data for safety and efficacy of warfarin. Higher dose may be needed in neonates and infants.

2. Infants and children:

• If baseline INR is 1–1.3, dose = 0.2 mg/kg/dose orally Q24 hr (max 7.5 mg/dose)^‡

• If baseline INR >1.3, liver dysfunction, postoperative cardiac Fontan procedure patients, NPO/poor nutrition, receiving broad-spectrum antibiotics, receiving medications causing significant drug/drug interactions, receiving medications with CYP2C9 enzyme inhibition (e.g., amiodarone, metronidazole, fluconazole, Bactrim), or slow metabolizer of warfarin, dose = 0.1 mg/kg/dose Q24 hr (max 5 mg/dose)

II. Days 2–4
Dose Adjustment for Goal INR of 2–3
Day 2		Day 3 and 4
INR Level	Action	INR Level	Action
1.1–1.3	Repeat initial dose	1.1–1.3	Repeat initial dose^∗
1.4–1.9	50% of initial dose	1.4–1.9	50% of initial dose^∗
≥2	Hold dose for 24 hr, then restart at 50% of initial dose	2–3	50% of initial dose^†
		3.1–3.5	25% of initial dose^†
		>3.5	Hold dose until INR <3.5, then restart at 50% of previous dose^†

III. Day 5 and Maintenance
Maintenance Dosing
≥5 Days
INR Level	Action
1.1–1.4	Increase weekly dose by 20%
1.5–1.9	Increase weekly dose by 10%
2–3	Continue current dose
3.1–3.5	Decrease weekly dose by 10%
>3.5	Hold dose, recheck INR daily until INR <3.5, then restart at 20% less than previous dose

^∗ If INR is not >1.5 on day 4, patient should be reassessed, and dose/kg should be adjusted on an individual basis.

† Consult pediatric hematology for patient-specific recommendations on reduced dosing.

‡ Reported average daily dose to maintain INR of 2–3 for infants is 0.33 mg/kg; for adolescents, 0.09 mg/kg; and for adults, from 0.04–0.08 mg/kg.

TABLE 14-13

Management of Excessive Warfarin Anticoagulation

INR <5 without serious bleeding	Hold warfarin. Recheck INR daily. When INR approaches therapeutic range, resume warfarin at lower dose and follow INR daily.^∗
INR ≥5 but <8 without serious bleeding	Hold warfarin. Recheck INR every 12–24 hr. If high risk for bleeding, consider low dose of vitamin K oral or IV (30 mcg/kg for patients <40 kg in weight; 1–2.5 mg for patients >40 kg). When INR approaches therapeutic range, resume warfarin at a lower dose.^∗
INR ≥8 without serious bleeding	Hold warfarin. Recheck INR every 6–12 hr. Give vitamin K orally (PO) or IV (30 mcg/kg for patients <40 kg in weight; 1–2.5 mg for patients >40 kg). INR reduction expected to occur within 12–24 hours with IV or 24–48 hours with PO vitamin K. Repeat vitamin K as necessary. When INR approaches therapeutic range, resume warfarin at a lower dose.^∗
Serious bleeding at any INR elevation	Hold warfarin. Monitor INR every 6 hr. Give vitamin K IV (2.5–5 mg). Vitamin K may be repeated as needed. Consider use of FFP (10–15 mL/kg IV), recombinant factor VIIa (16 mcg/kg IV), prothrombinase complex concentrate, or rhFVIIa (Novoseven) IV. Restart warfarin when INR approaches therapeutic range and when clinically appropriate at a lower dose.^∗
Life-threatening bleeding at any INR	Hold warfarin. Monitor INR every 2–4 hr. Administer vitamin K IV at 5–10 mg. Repeat vitamin K as needed. Transfuse FFP (10–15 mL/kg IV), consider rhFVIIa (Novoseven) or prothrombinase complex concentrate. Restart warfarin when INR approaches therapeutic range and when clinically appropriate at a lower dose.^∗

NOTE: Always evaluate for bleeding risks and potential drug interactions.
FFP, Fresh frozen plasma; INR, international normalized ratio; IV, intravenous; rhVIIa, activated recombinant human factor VII.

∗ Refer to Table 14-12.

(2) Warfarin prolongs PT, aPTT, and dRVVT. Warfarin reduces the activity of vitamin K–dependent factors (II, VII, IX, X, protein C and S).

e. Thrombolytic therapy should be considered for life- or limb-threatening thrombosis. Consult a hematologist.

NOTE: Children receiving anticoagulation therapy should be protected from trauma. Subcutaneous injections should be used when possible, and caution should be used with intramuscular injections. The use of antiplatelet agents and arterial punctures should be avoided.

BOX 14-4 MEDICATIONS THAT INFLUENCE WARFARIN THERAPY ^∗

Significant Increase in INR	Significant Decrease in INR
Amiodarone	Amobarbital
Anabolic steroids	Aprepitant
Bactrim (TMP/SMZ)	Butabarbital
Chloramphenicol	Carbamazepine
Disulfiram	Dicloxacillin
Fluconazole	Griseofulvin
Isoniazid	Methimazole
Metronidazole	Phenobarbital
Miconazole	Phenytoin
Phenylbutazone	Primidone
Quinidine	Propylthiouracil
Sulfinpyrazone	Rifabutin
Sulfisoxazole	Rifampin
Tamoxifen	Secobarbital

Moderate Increase in INR	Moderate Decrease in INR
Cimetidine	Atazanavir
Ciprofloxacin	Efavirenz
Clarithromycin	Nafcillin
Delavirdine	Ritonavir
Efavirenz
Itraconazole
Lovastatin
Omeprazole
Propafenone
Ritonavir

INR, International normalized ratio; TMP/SMZ, trimethoprim/sulfamethoxazole.

∗ Numerous medications not listed in this table can affect warfarin administration.

C. Bleeding Disorders (Fig. 14-3 and Box 14-5)

1. Differential diagnosis of bleeding disorders (Table 14-14 and Box 14-5)

2. Desired factor replacement goals in hemophilia (Table 14-15)

VI. Blood Component Replacement

A. Blood Volume

Requirements are age specific (Table 14-16).

B. Blood Product Components

1. RBCs: Decision to transfuse RBCs should be made with consideration of clinical symptoms and signs, degree of cardiorespiratory or CNS disease, cause and course of anemia, and options for alternative therapy, noting risks for transfusion-associated infections and reactions.

FIGURE 14-3 Differential diagnosis (DDX) of bleeding disorders. aPTT, Activated partial thromboplastin time; DIC, disseminated intravascular coagulation; PT, prothrombin time.

TABLE 14-14

Common Coagulation Disorders

Factor VIII deficiency (hemophilia A)^∗	Characteristics: X-linked recessive, prolonged aPTT, reduced factor VIII activity, normal PT and BT Treatment: a. Treat with factor VIII concentrate, preferably recombinant factor VIII to reduce risk of infection. b. Factor level recovers by 2% per 1 unit of factor VIII per kg of body weight (refer to Table 14-15). c. First dose has shorter half-life, so if redosing needed, second dose should be given after 4–8 hr. Subsequent doses can be given every 12 hr. d. Continuous infusion often desirable—example, surgical patients or those requiring prolonged therapy usually need 50 U/kg loading dose, followed by 3–5 U/kg/hr. e. For suspected intracranial bleeding, replace to 100% before diagnostic procedure (e.g., computed tomography [CT] scan). f. Dose calculation: units of factor VIII needed = weight (kg) × desired % replacement × 0.5.
Factor IX deficiency (hemophilia B or Christmas disease)^∗	Characteristics: X-linked recessive, prolonged aPTT, reduced factor IX activity Treatment: a. Treat with factor IX concentrate, preferably recombinant to reduce risk of infection. b. Factor level usually recovers by 1% for each unit of factor IX concentrate per kg of body weight. c. Half-life of factor IX 18–24 hr. Similar to factor VIII, if second dose needed, it should be given at a shorter interval. d. Recombinant factor IX has a shorter half-life; consider evaluation of in vivo factor survival in patient. e. Replace to 100% before diagnostic procedure if intracranial bleeding is suspected. f. Dose calculation: units of factor IX needed = weight (kg) × desired % replacement (may be advisable to multiply by 1.2 for recombinant factor IX).
Table Continued

von Willebrand disease

Characteristics: vWF binds platelets to subendothelial surfaces and carries and stabilizes factor VIII.

Type 1: Decreased activity of vWF and proportionally decreased quantity of vWF. Mild to moderate bleeding. Prolonged BT, normal platelet count, platelet dysfunction on platelet function testing, aPTT normal in most cases but may be mildly prolonged.

Type 2: Characterized by four subtypes, all with various functional abnormalities of vWF. Mild to moderate bleeding but in some cases can be severe.

Type 3: Absence or near absence of vWF, with reduction of factor VIII and severe bleeding.

Treatment:

a. Majority of patients with type 1 vWD respond to DDAVP (desmopressin acetate) with increases in vWF activity from two- to threefold over baseline (DDAVP responsiveness should be established by prior testing). IV or intranasal DDAVP may be used for minor bleeding or surgical procedures.

b. DDAVP may be contraindicated in the rare vWD type 2B, because it may exacerbate thrombocytopenia.

c. For more severe disease or patients who do not respond to DDAVP, treatments of choice are purified plasma-derived products containing both vWF and factor VIII (HUMATE P, Alphanate, or Wilate). These concentrates are preferred because they are virally inactivated.

d. Aminocaproic acid 100 mg/kg IV or PO every 4–6 hr (up to 30 g/day) may be useful for treatment of mucosal bleeding and as prophylaxis for dental extraction.

aPTT, Activated partial thromboplastin time; BT, bleeding time; IV, intravenous; PO, per os; PT, prothrombin time; vWF, von Willebrand factor
.

∗ All patients with hemophilia should be vaccinated with hepatitis A and B vaccines.

TABLE 14-15

Desired Factor Replacement in Hemophilia

Bleeding Site	Desired Level (%)
Minor soft tissue bleeding	20–30
Joint	40–70
Simple dental extraction	50
Major soft tissue bleeding	80–100
Serious oral bleeding	80–100
Head injury	100+
Major surgery (dental, orthopedic, other)	100+

NOTE: A hematologist should be consulted for all major bleeding and before surgery.
Round to the nearest vial; do not exceed 200%.

BOX 14-5 ACQUIRED COAGULOPATHIES

Disseminated intravascular coagulation: Characterized by prolonged PT and aPTT, decreased fibrinogen and platelets, increased fibrin degradation products, and elevated D-dimer. Treatment includes identifying and treating underlying disorder. Replacement of depleted coagulation factors with FFP may be necessary in severe cases, especially when bleeding is present; 10–15 mL/kg will raise clotting factors 20%. Fibrinogen, if depleted, can be given as cryoprecipitate. Platelet transfusions may also be necessary.

Liver disease: Liver is the major site of synthesis of factors V, VII, IX, X, XI, XII, XIII, prothrombin, plasminogen, fibrinogen, protein C and S, and ATIII. Treatment with FFP and platelets may be needed, but this will increase hepatic protein load. Vitamin K should be given to patients with liver disease and clotting abnormalities.

Vitamin K deficiency: Factors II, VII, IX, X, protein C, and protein S are vitamin K dependent. Early vitamin K deficiency may present with isolated prolonged PT because factor VII has the shortest half-life. Fibrinogen should be normal.

aPTT, Activated partial thromboplastin time; CNS, central nervous system; DIC, disseminated intravascular coagulation; FFP, fresh frozen plasma; PT, prothrombin time.

a. Packed RBC (PRBC) transfusion: Concentrated RBCs with HCT of 55%–70%. A typed and cross-matched blood product is preferred when possible; O-negative (or O-positive) blood may be used if transfusion cannot be delayed. O-negative is preferred for females of childbearing age to reduce risk for Rh sensitization.

(1) Unless rapid replacement is required for acute blood loss or shock, infuse no faster than 2–3 mL/kg/hr (generally 10–15 mL/kg aliquots over 4 hr) to avoid congestive heart failure.

(2) Rule of thumb in severe compensated anemia: Give an X mL/kg aliquot, where X = patient Hb (g/dL); for example, if Hb = 5 g/dL, transfuse 5 mL/kg over 4 hours.

(3) To calculate the volume of PRBC to achieve a desired HCT, use the following equation:

Volume of PRBCs(mL)=EBV(mL)× (desired HCT−actual HCT)HCT of PRBCs

where EBV is the estimated blood volume (see Table 14-16 for age-specific EBV) and HCT of PRBCs is usually 55%–70%

(4) A unit of blood is 500 mL, but approximately 300 mL after processing without significant loss of red cells. This may vary with type of diluents used and time of storage, owing to red cell compaction.

b. Leukocyte-poor PRBCs:

(1) Filtered RBCs: 99.9% of WBCs removed from product; used for cytomegalovirus (CMV)-negative patients to reduce risk for CMV transmission. Also reduces likelihood of a nonhemolytic febrile transfusion reaction.

(2) Washed RBCs: 92%–95% of WBCs removed from product. Similar advantages to leukocyte-poor filtered RBCs. Although filtered leukocyte-poor blood is now more commonly used, washing may be helpful if a patient has preexisting antibodies to blood products (e.g., patients who have complete IgA deficiency or history of urticarial transfusion reactions).

TABLE 14-16

Estimated Blood Volume (EBV)

Age	Total Blood Volume (mL/kg)
Preterm infants	90–105
Term newborns	78–86
1–12 mo	73–78
1–3 yr	74–82
4–6 yr	80–86
7–18 yr	83–90
Adults	68–88

Data from Nathan D, Oski FA. Hematology of Infancy and Childhood. Philadelphia: WB Saunders, 1998.

c. Irradiated blood products:

(1) Many blood products (PRBCs, platelet preparations, leukocytes, FFP, and others) contain viable lymphocytes capable of proliferation and engraftment in the recipient, causing graft-versus-host disease (GVHD). Irradiation with 1500 cGy before transfusion may prevent GVHD but does not prevent antibody formation against donor white cells. Engraftment most likely in young infants, immunocompromised patients, and patients receiving blood from first-degree relatives.

(2) Indications: Intensive chemotherapy, leukemia, lymphoma, bone marrow transplantation, solid organ transplantation, known or suspected immune deficiencies, intrauterine transfusions, and transfusions in neonates.

d. CMV-negative blood: Obtained from donors who test negative for CMV. May be given to neonates or other immunocompromised patients, including those awaiting organ or marrow transplant who are CMV negative.

2. Platelets: Indicated to treat severe or symptomatic thrombocytopenia. Should not be refrigerated because this promotes premature platelet activation and clumping. Bacteremia secondary to contamination more common than with refrigerated blood products.

a. Single-donor product: Preferred over pooled concentrate for patients with antiplatelet antibodies.

b. Leukocyte-poor: Use if there is a history of significant acute febrile platelet transfusion reactions.

c. Usually give 4 U/m², or approximately 10 mL/kg of normally concentrated platelet product. Platelet count is raised by 10,000 to 15,000/µL by giving 1 U/m². For infants and children, 10 mL/kg will increase platelet count by about 50,000/µL.

d. Hemorrhagic complications are rare with platelet counts >20,000/µL. A transfusion trigger of 10,000/µL is recommended by many in the absence of serious bleeding complications. Platelet count >50,000/µL is advisable for minor procedures; >100,000/µL is advisable for major surgery or intracranial operation.

e. Usually unit = 50 mL after processing, ≥5.5 × 10¹¹plt/unit.

3. FFP: Contains all clotting factors except platelets. Used in severe clotting factor deficiencies with active bleeding or in combination with vitamin K to achieve rapid reversal of effects of warfarin. Also replaces anticoagulant factors (antithrombin III, protein C, protein S). Used in treatment of DIC, vitamin K deficiency with active bleeding, orTTP. One milliliter of FFP expected to provide 1 unit of activity of all factors except labile factor V and VIII, but individual units may vary. Usual amount is 10–15 mL/kg; repeat doses as needed. In acquired TTP, plasma exchange is the treatment of choice. Usually unit = 250–300 mL after processing.

4. Cryoprecipitate: Enriched for factor VIII (5–10 U/mL), vWF, and fibrinogen. Historically useful for children with factor VIII or vWF deficiency in the context of active bleeding, but concentrates or recombinant products now preferred because of lower risk for viral transmission. Useful for raising fibrinogen when small volumes are required. Usually unit = 10–15 mL after processing (80 units factor VIII and 250 mg fibrinogen).

5. Monoclonal factor VIII: Highly purified factor derived from pooled human blood using monoclonal antibodies.

6. Recombinant factor VIII or IX: Highly purified with less (theoretical)infectious risk than pooled human products. There is risk for inhibitor formation, as with other products.

C. PRBC Exchange Transfusion

1. Partial PRBC exchange transfusion may be indicated for sickle cell patients with acute chest syndrome, stroke, intractable pain crisis, or refractory priapism. Replace with Sickledex-negative cells. Follow HCT carefully during transfusion to avoid hyperviscosity, maintaining HCT <35%.

2. Indications for double packed volume PRBC exchange transfusion include severe acute chest and CVA. This is based on twice the patient’s calculated packed cell volume. Goal is to reduce percentage of HbS to <30%. Expected reduction in percentage of circulating sickle cells is 60%–80%.

3. To calculate the volume of PRBC needed for a double packed volume PRBC exchange, use the following equation:

Desired volume of exchange=EBV(mL)× Patient HCT×2/(HCT of PRBC)

where EBV is the age-dependent estimated blood volume (see Table 14-16), and HCT of PRBC is 55%–70%.

D. Complications of Transfusions

1. Acute transfusion reactions:

a. Acute hemolytic reaction: most often the result of blood group incompatibility. Signs and symptoms include fever, chills, tachycardia, hypotension, and shock. Treatment includes immediate cessation of blood transfusion and institution of supportive measures. Laboratory findings include DIC, hemoglobinuria, and positive Coombs test.

b. Febrile nonhemolytic reaction: Usually the result of inflammatory cytokines; common in previously transfused patients. Symptoms include fever, chills, and diaphoresis. Stop transfusion and evaluate. Prevention includes premedication with antipyretics, antihistamines, corticosteroids, and if necessary, use of leukocyte-poor PRBCs.

c. Urticarial reaction: Reaction to donor plasma proteins. Stop transfusion immediately; treat with antihistamines, and epinephrine and steroids if there is respiratory compromise (see also treatment of anaphylaxis, Chapter 1). Use washed or filtered RBCs with the next transfusion.

d. Evaluation of acute transfusion reaction:

(1) Patient's urine: Test for hemoglobin.

(2) Patient's blood: Confirm blood type, screen for antibodies, and repeat direct Coombs test (DCT) on pretransfusion and posttransfusion sera.

(3) Donor blood: Culture for bacteria.

2. Delayed transfusion reaction: Usually due to minor blood group antigen incompatibility, with low or absent titer of antibodies at time of transfusion. Occurs 3–10 days after transfusion. Symptoms include fatigue, jaundice, and dark urine. Laboratory findings include anemia, positive Coombs test, new RBC antibodies, and hemoglobinuria. The need for acute intervention is much less likely than with acute reactions.

3. Transmission of infectious diseases⁶^,^,10: Blood supply is tested for HIV types 1 and 2, HTLV types I and II, hepatitis B, hepatitis C, syphilis, and West Nile virus. Data from 2009 Red Book estimate the risk for transmitting infection (estimated per unit) as follows: HIV (1 in 2,000,000); HTLV (1 in 641,000); hepatitis B (1 in 63,000–500,000); hepatitis C (1 in 100,000); parvovirus (1 in 10,000). CMV, hepatitis A, parasitic, tickborne, and prion diseases may also be transmitted by blood products.

4. Sepsis: Occurs with products contaminated with bacteria, particularly platelets, because they are stored at room temperature. Risk for transmitting bacteria in PRBCs is 1 in 5 million units, and in platelets is 1 in 100,000.

E. Reasons Not to Consider a Directed Donor

1. Donors less likely to be truthful about risk

2. Increase risk of transfusion-related GVHD if from a relative

3. Can alloimmunize if potential bone marrow donor

F. Reasons to Consider a Directed Donor

1. Chronic transfusion programs (e.g., thalassemia or sickle cell disease), where donors provide antigen-matched red cells repetitively for the same patient

2. NAIT, where maternal platelets lack causative antigens and represent optimal therapy

VII. Interpreting Blood Smears

See Figures 14-4 through 14-15 for examples of blood smears. Examine the blood smear in an area where the RBCs are nearly touching but do not overlap.

A. RBC

Examine size, shape, and color.

B. WBC

A rough estimate of the WBC count can be made by looking at the smear under high power (×100 magnification). Each one cell per high-power field correlates with approximately 500 WBC/mm³ (×20 magnification).

C. Platelets

A rough estimate of platelet count is one platelet per high-power field corresponds to 10,000–15,000/µL. Platelet clumps usually indicate >100,000 platelets/µL.