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.