Recognition of rare hemoglobin variants by hemoglobin A_1c measurement procedures

Background Unrecognized hemoglobinopathies can lead to measured hemoglobin A_1c (Hb A_1c) concentrations that are erroneous or misleading. We determined the effects of rare hemoglobin variants on capillary electrophoresis (CE) and HPLC methods for measurement of Hb A_1c. Methods We prospectively investigated samples in which Hb A_1c was measured by CE during a 14-month period. For samples in which the electropherograms suggested the presence of rare hemoglobinopathies, hemoglobin variants were identified by molecular analysis or by comparison with electropherograms of known variants. When sample volume permitted, Hb A_1c was measured by 2 HPLC measurement procedures and by boronate affinity HPLC. Results Hb A_1c was measured by CE in 33,859 samples from 26,850 patients. 15 patients (0.06%) were identified as having rare hemoglobinopathies: Hbs A2 prime, Agenogi, Fannin-Lubbock I, G Philadelphia, G San Jose, J Baltimore, La Desirade, N Baltimore, Nouakchott, and Roanne. Among 6 of these samples tested by 2 ion-exchange HPLC methods, the rare Hb was detected by both HPLC methods in only one sample, and none were detected by boronate affinity HPLC. The mean of the Hb A_1c results of 2 HPLC methods differed from the result of the CE method by 0.7–2.2% Hb A_1c in samples with variant hemoglobins versus < 0.2% Hb A1c in samples without variants. Conclusion Measurement procedures differ in the ability to detect the presence of rare Hb variants and to quantify Hb A_1c in patients who harbor such variants.