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/ß⁰-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 [3.7 kb deletion (-a^3.7)] was detected by polymerase chain reaction. Patients were classified as homozygous (-a^3.7/-a^3.7), heterozygous (-a^3.7/a), 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.

Hemoglobin A₂ ; Alpha thalassemia; Beta thalassemia; Sickle cell disease; High performance liquid chromatography