HbA(1c)--an analyte of increasing importance.

Since the incorporation in 1976 of HbA(1c) into a monitoring program of individuals with diabetes, this test has become the gold standard for assessment of glycemic control. Analytical methods have steadily improved in the past two decades, largely through the efforts of the National Glycohemoglobin Standardization program (NGSP). The new definition of HbA(1c) and the introduction of an analytically pure calibrator have increased the possibility for greater improvements in analytical performance. Controversies exist in the reporting of HbA(1c). The use of HbA(1c) has expanded beyond the use solely as a measure of glycemic control into a test for screening and diagnosing diabetes. With improvements in analytical performance, the effects of demographic factors such as age and ethnicity and clinical factors such as iron deficiency have been observed. In this review, the history, formation, analytical methods and parameters that affect HbA(1c) analysis are discussed.