Verification of Capillary Electrophoresis Method for Hemoglobin A1c Measurement Hemoglobin A1c is the leading marker of glycemic control. Determination of its concentration is of great importance for diagnosing, monitoring therapy and course of diabetes. Results of performance evaluation of the Sebia Minicap Flex Piercing in accordance with protocol CLSI EP05-A2 are shown with the aim to introduce capillary electrophoresis as the method for measurement of hemoglobin A1c into routine work. Commercial control samples and a mixture of human samples from patients in two concentration levels, in triplicate during five days, were used to test imprecision and inaccuracy of the method. In order to estimate the comparability with the method currently in use (TINIA, on the Siemens Dimension ExL) 117 samples from patients of KBC Osijek were used, venous blood sampled on K–EDTA anticoagulant. The stability of the samples was tested by comparison to results from capillary electrophoresis of 113 samples before and after freezing. Results are expressed in IFCC (mmol/mol) and NGSP (%) units. Capillary electrophoresis on the Sebia Minicap Flex Piercing fulfills strict clinical criteria for imprecision and inaccuracy. The low coefficient of variation and mean value of bias for both concentration levels is lower than the clinically significant (2%, 3 mmol/mol). The constant and proportional difference between the two methods is higher than clinically significant. The TINIA method yields lower results, especially in high concentrations, therefore both methods cannot be used concurrently. 20% of results from frozen samples are clinically significantly lower, and samples of K-EDTA whole blood cannot be stored at -20°C. Capillary electrophoresis is suitable for quantifying hemoglobin A1c for diagnosing diabetes and monitoring therapy and glycemic status. Other forms of hemoglobin do not interfere with the method and it is also suitable for screening hemoglobinopathy and thalassemia.