The effect of sequentially removing subjects with iron deficiency, the α-thalassemia -3.7-kb allele, sickle trait, and serum creatinine levels of more than 1.4 mg/dL on the hemoglobin level (Hb) of African-American men and women and of age- and sex-matched white controls. Top graph, women; bottom graph, men. Fe def indicates iron deficiency; Thal, α-thalassemia -3.7-kb allele; S, sickle trait; and Creat, serum creatinine levels of more than 1.4 mg/dL. Error bars indicate SEM.