Chapter 10

Anemia

Key Teaching Points

I. Introduction

II. The Findings

Chronic anemia causes the skin and conjunctiva to appear abnormally pale because of reduced amounts of red-colored oxyhemoglobin that circulate in the dermal and subconjunctival capillaries and venules.1 Nonetheless, pallor does not always indicate anemia, because skin color also depends on the diameter of these minute vessels, the amount of circulating deoxyhemoglobin, and the patient’s natural skin pigments.1 Vasoconstriction from cold exposure or sympathetic stimulation also may cause pallor, and the pallor of anemia may be obscured by the red color of vasodilation (inflammation or permanent vascular injury from ischemia, cold, or radiation), the blue color of cyanosis (see Chapter 9), or the brown pigments of dark-skinned persons. Theoretically, examination of the conjunctiva, nailbeds, and palms avoids the effects of the patient’s natural skin pigments.
Most clinicians assess for pallor subjectively by comparing the patient’s skin color with their own color or their recollection of normal skin color. One definition of pallor, however, is more objective: conjunctival rim pallor is present if examination of the inferior conjunctiva reveals the color of the anterior rim to have the same pale fleshy color of the deeper posterior aspect of the palpebral conjunctiva (Fig. 10.1).2 In persons without anemia, the normal bright red color of the anterior rim contrasts markedly with the fleshy color of the posterior portion.
image
FIG. 10.1 Conjunctival rim pallor.
After gently pulling down the patient’s lower lid (top), the clinician observes the lid’s inner surface, comparing the color of the lid margin (its rim) with the conjunctival surface nearer to the globe. In patients without anemia (bottom left), there are two zones of color: a reddish color at the rim (due to its prominent vascular supply) and a contrasting paler color nearer to the globe (from prominent lymphoid tissue). In patients with anemia (bottom right), the entire inner surface of the lower lid has a pale color (conjunctival rim pallor).

III. Clinical Significance

EBM Box 10.1 presents the diagnostic accuracy of physical signs for chronic anemia as applied to hundreds of patients. These studies excluded patients with acute bleeding or those who had recently received transfusions. As much as possible, the color of skin and conjunctiva was determined using natural lighting.
According to EBM Box 10.1, the finding of conjunctival rim pallor (likelihood ratio [LR] = 16.7) increases the probability of anemia the most, followed by palmar crease pallor (LR = 7.9), palmar pallor (LR = 5.6), conjunctival pallor (i.e., not specifically conjunctival rim pallor, LR = 4.7), pallor at any site (LR = 3.8), facial pallor (light-skinned persons only, LR = 3.8), and tongue pallor (LR = 3.7). Nailbed pallor lacks diagnostic value (LR not significant). Importantly, no physical sign convincingly decreases the probability of anemia (i.e., no LR <0.4).