Chromatographic measurements of hemoglobin A2 in blood samples that contain sickle hemoglobin

Abstract

In the sickle cell syndromes, Hb A2 measurements aid in the differential diagnosis of sickle cell anemia from sickle-beta-thalassemia. The purpose of this study is to assess the Hb A2 levels in samples containing sickle hemoglobin (Hb S) by the use of an automated high performance liquid chromatography system (HPLC-Variant beta-thalassemia Short Program). The blood samples analyzed were from individuals of African descent living in the state of Tennessee who had either sickle cell trait (Hb AS), sickle cell disease (Hb SS), or sickle cell-hemoglobin C disease (Hb SC). Interestingly, the Hb A2 levels determined by HPLC were found elevated in samples containing Hb S. The Hb A2 mean in Hb AS samples (n=146) is 4.09% (SD +/- 0.42, range 2.20 to 5.20%); in Hb SS samples (n=33) it is 3.90% (SD +/- 1.08, range 0.60 to 5.90%); and in Hb SC samples (n=27) it is 4.46% (SD +/- 0.70, range 2.30 to 5.91%). The Hb A2 mean by HPLC in normal individuals (Hb AA, n=70) is 2.57% (SD +/- 0.25, range 2.1 to 3.0%), and the Hb A2 range in beta-thalassemia carriers is 4 to 9%. Our results show that the Hb A2 levels in Hb S-containing samples partially overlap with those expected from beta-thalassemia carriers. The hemoglobinopathy laboratory should be aware of this apparent elevation in Hb A2 levels determined by HPLC in individuals carrying Hb S. Other factors, such as family history and clinical symptoms, should be taken into account before a diagnosis of sickle cell trait, sickle-beta-thalassemia, or sickle cell anemia is made.