The effect of Hb F and α‐thalassemia on the red cell indices in sickle cell anemia

This study examines the effect of different levels of fetal hemoglobin (Hb F) and the presence or absence of genes for α‐thalassemia on the red cell indices and degree of anemia among 102 patients with homozygous sickle cell disease (S/S) between the ages of 15 and 62 years. Patients were divided into those with an average Hb F of < 10 gm/L („low”︁ Hb F group) and those with > 10 gm/L („high”︁ Hb F group). α‐Thalassemia was assessed by restriction enzyme analysis of DNA by the Southern blotting technique. Homozygosity for the βs gene was confirmed by restriction enzyme analysis of DNA using the enzyme Mst II. There were 51 patients with four α‐globin genes, 28 of whom had „high”︁ and 23 „low”︁ Hb F levels. Fifty‐one patients had α‐thalassemia, 38 of whom were heterozygous and 13 homozygous for the 3. 7 kb α‐thalassemia deletion. Nine had „high”︁ and 31 had „low”︁ Hb F. Irrespective of α‐globin genotype, patients in the high Hb F group had a higher mean Hb, Hct, MCV, and MCH than those in the low HB F group. In patients without α‐thalassemia Hb F was positively correlated with MCV and MCH (p < 0.001), patients with high Hb F levels having macrocytosis confirmed by microhematocrit studies. Patients with α‐thalassemia had a lower MCHC than patients with four α‐globin genes and this was not significantly affected by the level of Hb F. The combination of α‐thalassemia and high levels of Hb F appears to result in a distinctive S/S phenotype that is similar to the type of S/S disease described in Southern India.