With the publication of the results of the landmark 9-year Diabetes Control and Complications Trial (DCCT), the importance of Hb A1c/glycohemoglobin testing in diabetes was firmly established. The DCCT showed, at least in patients with insulin-dependent diabetes mellitus, that the risk for development and progression of the chronic complications of diabetes is closely related to the degree of metabolic control as measured by glycohemoglobin determinations (1). Generally, the same is believed to be true for patients with non-insulin-dependent diabetes mellitus, although the results of the UK Prospective Study must be awaited (2)(3). The DCCT has confirmed that measuring glycohemoglobin in blood is an excellent tool for the long-term control of the glycemic state. Considering the high prevalence of diabetes mellitus, glycohemoglobin is one of the most important analytes in laboratory medicine today (4). A major task of clinical chemistry should be to optimize conditions for its determination. The development of new methodologies and international standardization is an essential part of such efforts. Despite the ongoing efforts for standardization of Hb A1c/glycohemoglobin (5), many glycohemoglobin assays are not standardized among clinical laboratories; values reported by one laboratory may not agree with those from another, and possibly neither would agree with those from the DCCT (6). Glycohemoglobins are the products of a nonenzymatic reaction between the free aldehyde group of glucose (Hb A1c) or other sugars and the unprotonated form of free amino groups of hemoglobin. The percentage of glycohemoglobin in human blood depends on the concentration of glucose, the duration of glucose exposure to hemoglobin, and the turnover of erythrocytes. The higher the glucose concentration and the longer the exposure time, the higher the percentage of Hb A1c. The potential glycation sites of the hemoglobin A molecule are the N-terminal …