Evaluation and interference study of hemoglobin A1c measured by turbidimetric inhibition immunoassay

The technical performance of the turbidimetric immunoinhibition (TI) assay for hemoglobin (Hb) Al-1c (Tina-quant Hb A(1c), Boehringer Mannheim, Indianapolis, Ind) was evaluated by using the BM/Hitachi 911 analyzer. Intra-assay imprecision was less than 2.7%, and interassay imprecision was less than 2.8% as measured by coefficient of variation. In 93 subjects with diabetes who did not have hemoglobin variants, results of the TI assay for Hb A(1c) correlated strongly with those obtained by using a highperformance liquid chromatography analyzer (Diamat, BioRad Laboratories, Hercules, Calif). Among 241 subjects who had or did not have hemoglobin variants, the TI assay for Hb A(1c) correlated strongly with results of affinity chromatography for total glycated hemoglobin (Glyc-Affin GHb, IsoLab, Akron, Ohio). We also studied the effect of various percentages of hemoglobin S, C, E, and F on the accuracy of the TI Hb A(1c) assay. Only high hemoglobin F percentages caused interference. More than 14 times as many samples can be analyzed per hour by using the TI Hb A(1c) assay than can be analyzed by using the HPLC assay. For high-volume reference laboratories, using the fully automated TI Hb A(1c) assay to monitor glycemic control in patients with diabetes may be preferable to using the conventional ion-exchange highperformance liquid chromatography Hb A(1c) assay because the TI assay measures Hb A(1c) more accurately in patients with diabetes who have hemoglobin variants, and it requires less time.