Hemoglobin A2 values in sickle cell disease patients quantified by high performance liquid chromatography and the influence of alpha thalassemia

BACKGROUND In sickle cell disease, the quantification of Hb A2 is important for the differential diagnosis between sickle cell anemia (Hb SS) and Hb S/β(0)-thalassemia. OBJECTIVE To determine Hb A2 levels as quantified by high performance liquid chromatography in patients with sickle cell anemia (Hb SS) and with the SC hemoglobinopathy, with or without concomitant alpha thalassemia. METHODS This is a retrospective study of 242 children aged between two and six years with diagnoses of Hb SS or Hb SC. The hemoglobin was evaluated using high performance liquid chromatography and alpha thalassemia [3.7kb deletion (-α(3.7))] was detected by polymerase chain reaction. Patients were classified as homozygous (-α(3.7)/-α(3.7)), heterozygous (-α(3.7)/α), or homozygous wild-type. Analysis of variance was used to compare the mean Hb A2 values between the alpha thalassemia groups. RESULTS The mean (±standard deviation) Hb A2 concentrations in the Hb SS group (n=135) was 3.68±0.65%. The mean values for individuals with Hb SS and heterozygous (n=28) or homozygous for alpha thalassemia (n=3) were 3.98±0.64% and 4.73±0.25%, respectively. The mean Hb A2 of all the Hb SC patients (n=107) was 4.01±0.507 with 4.29±0.41% and 4.91±0.22% in individuals heterozygous (n=23) and homozygous for alpha thalassemia (n=7), respectively. All patients homozygous for alpha thalassemia had Hb A2 levels above 3.5%. However, Hb A2 values above 5.2% were seen in patients with Hb SS and Hb SC, independently of alpha thalassemia. CONCLUSION Hb A2 levels are elevated in patients with Hb S or Hb C, and are directly influenced by the alpha thalassemia genotypes.