Hemoglobin Variants and Hemoglobin A1c Analysis: Problem Solved? Measurement of glycohemoglobin (GHb) is an integral

component of the management of patients with diabetes mellitus (1, 2). Glycation is the nonenzymatic addition of a sugar residue to amino groups of proteins. Numerous proteins in the body are glycated, but GHb in blood is the analyte most widely used clinically to monitor glycemic control. The concentration of GHb is directly proportional to the mean concentration of glucose in the blood and the lifespan of erythrocytes (mean, 120 days). Thus, the GHb concentration represents an integrated value for glucose over the preceding 2–3 months. GHb provides an index of glycemic control that is free of the wide diurnal glucose fluctuations and is unaffected by recent exercise or food ingestion. Two large, prospective, randomized clinical trials dem-onstrated a strong relationship between hyperglycemia and the development of microvascular complications of diabetes. In the Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS), which studied patients with type 1 and type 2 diabetes, respectively (3, 4), glycemic control was assessed by GHb. Both studies established a direct rela-tionship between the GHb concentration and the risk of complications. These findings led the American Diabetes Association to recommend that a primary treatment goal in adults with diabetes should be near-normal glycemia with hemoglobin A1c (HbA1c) 7 % when measured by the method used for the DCCT (2). The recommendation that HbA1c be measured at least every 6 months in patients with type 1 or type 2 diabetes (2) has had a dramatic impact on the use of this test. The number of laboratories participating in the GHb surveys offered b