Few point-of-care hemoglobin A1c assay methods meet clinical needs.

Accurate and timely measurements of hemoglobin A1c (Hb A1c) 2 are an increasingly important challenge for clinical laboratories. As Hb A1c measurements are being used to answer new clinical questions, each new use of Hb A1c imposes requirements for the analytical performance of the methods used to measure it. Until recently, Hb A1c was used only as a key test for monitoring glycemic control in people with diabetes. More recently, it has been proposed as the preferred test for the diagnosis of diabetes (1, 2 ), and it is being used in many areas to calculate an estimated average glucose (eAG) concentration (3, 4 ). The analytical requirements differ in these 3 uses of the test. In monitoring glycemic control, as with any test used for monitoring therapy, the reproducibility of Hb A1c assays is critical. Freedom from bias, however, has also become critical, because fixed cutpoints are being used as targets for glycemic control. When Hb A1c is used for measuring eAG concentrations, errors in the measurement may produce unexpectedly large changes in eAG. In the diagnosis of diabetes, fixed cutpoints are used, again requiring particular attention to the effect of bias on diagnostic accuracy. In addition to analytical requirements, there is pressure for rapid return of results in view of evidence that improved glycemic control can be achieved when Hb A1c results are made available at the point of care (POC) (5, 6). It is against this background that an important new report addresses the analytical performance of POC assays for Hb A1c. In this issue of Clinical Chemistry, Lenters-Westra and Slingerland (7) report on the imprecision, bias, and total error of 8 POC Hb A1c analyzers. The study used well-defined protocols from the CLSI and 3 appropriate secondary reference measurement procedures. Two of the 8 manufacturers withdrew from the study after initial unpromising results with their POC methods. Only 2 methods met an acceptance criterion of a total CV 3% in the clinically relevant concentration range, and only these 2 methods met the 0.85% error criterion of the National Glycohemoglobin Standardization Program (NGSP) with 2 different lots of reagent. These results have important clinical implications for monitoring therapy, calculating the eAG, and diagnosing diabetes or estimating the risk of developing diabetes.