Abstract

Aims: To assess the accuracy and precision of measuring haemoglobin A₂ by high performance liquid chromatography (HPLC) in the presence and absence of sickle cell trait, with or without α thalassaemia trait.

Methods: The haemoglobin A₂ percentage and the haemoglobin A₂ plus S percentages were determined by HPLC on 82 normal controls and 78 patients with sickle cell trait, respectively; the α thalassaemia status of each patient was determined by polymerase chain reaction. Red cell indices and haemoglobin A₂ and S percentages were compared in patients with two, three, or four α genes.

Results: Of the 78 patients with sickle cell trait, 17 were heterozygous for α⁺ thalassaemia (−α^3.7/αα) and 13 were homozygous (−α^3.7/−α^3.7). Microcolumn chromatography showed that the haemoglobin A₂ percentage was slightly, but significantly, higher than normal in sickle cell trait. HPLC determinations of haemoglobin A₂ percentage in patients with sickle cell trait are precise but inaccurate, the percentage being appreciably overestimated. The measured haemoglobin A₂ percentage is stable for one week, but inaccuracy increases by two weeks in most samples. Despite this inaccuracy, there are significant differences in the HPLC “haemoglobin A₂ percentage” between groups of individuals with two, three, and four α genes.

Conclusions: Haemoglobin A₂ determinations by HPLC are precise but inaccurate. Nevertheless, there are significant differences in the haemoglobin A₂ percentage in subjects with two, three, and four α genes. Although there is some overlap between groups, this can be useful, together with the red cell indices, in predicting the likelihood of coexisting α thalassaemia.