Quantitation of hemoglobin A2. An interlaboratory study.

In the 1976 hemoglobinopathy proficiency testing survey of the Center for Disease Control (CDC), whole-blood samples from hematologically normal adults and from individuals heterozygous for beta-thalassemia were shipped to survey participants. The object of this survey was to determine the state of the art for technics used to quantitate hemoglobin A2 (Hb A2) and to test the ability of laboratories to differentiate between blood samples having normal Hb A2 levels and those having elevated levels (i.e., those from individuals with beta-thalassemia trait). The results of Hb A2 quantitation obtained from 183 volunteer participant laboratories were compared with those obtained from 24 reference laboratories. Individual values varied greatly among laboratories and among methods for both normal and elevated Hb A2 samples. The results returned by many laboratories were not within 2 SD of the reference laboratory mean and also were not sufficiently accurate to differentiate between the normal blood samples and those with beta-thalassemia trait. The results suggest that methods for quantitating Hb A2 need to be standardized and a suitable method for determining laboratory performance found.