Hematologic differences between African-Americans and whites: the roles of iron deficiency and alpha-thalassemia on hemoglobin levels and mean corpuscular volume

Abstract

The average results of some laboratory measurements, including the hemoglobin, mean corpuscular volume (MCV), serum transferrin saturation (TS), serum ferritin, and white blood cell count of African-Americans differ from those of whites. Anonymized samples and laboratory data from 1491 African-American and 31 005 white subjects, approximately equally divided between men and women, were analyzed. The hematocrit, hemoglobin, MCV, TS, and white blood cell counts of African-Americans were lower than those of whites; serum ferritin levels were higher. When iron-deficient patients were eliminated from consideration the differences in hematocrit, hemoglobin, and MCV among women were slightly less. The -3.7-kilobase alpha-thalassemia deletion accounted for about one third of the difference in the hemoglobin levels of African-Americans and whites and neither sickle trait nor elevated creatinine levels had an effect. Among all subjects, 19.8% of African-American women would have been classified as "anemic" compared with 5.3% of whites. Among men, the figures were 17.7% and 7.6%. Without iron-deficient or thalassemic subjects, the difference had narrowed to 6.1% and 2.77% and to 4.29% and 3.6%, respectively. Physicians need to take into account that the same reference standards for hemoglobin, hematocrit, MCV, and TS and the white blood cell count do not apply to all ethnic groups.

Figure 1.

The blood hemoglobin concentration, MCV, TS, and serum ferritin of 598 African-American men and women and more than 12 000 age-matched white controls attending a Health Appraisal Clinic. The African-American subjects profiled in the figure were attending a Health Appraisal Clinic and were genotyped for α-thalassemia and hemoglobin S. The error bars represent one standard error of the mean. (A) All subjects without exclusions. (B) Subjects after removing those with iron deficiency (see “Patients, materials, and methods”). AA indicates African-American. Error bars indicate standard error of the mean (SEM).

Figure 2.

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.