Figure 1. Percentage of children with sickle cell disease who had any of the listed health problems as a function of plasma retinol concentration below normal (<20 μg/dL) and within the normal range (≥20 μg/dL). A higher percentage of children with plasma retinol <20 μg/dL vs children with levels ≥20 μg/dL had pain crisis episodes (chi-square test, a>b, P < 0.05) or inflammation (*P = 0.1). For all other measurements, no significant differences were detected.