Psychological Impact of Changing the Scale of Reported HbA1c Results Affects Metabolic Control

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Abstract
HbA1c has been an invaluable tool for the monitoring of long-term complications in type 1 and type 2 diabetes. However, in spite of the wide international use of HbA1c, there has been a substantial lack of harmonization among methods (1). Both the Diabetes Control and Complications Trial (DCCT) (2) and the U.K. Prospective Diabetes Study (UKPDS) (3) used the same method for analysis of HbA1c and, with the help of the National Glycohemoglobin Standardization Program (NGSP), many HbA1c methods have been standardized to the results reported in these landmark trials (4). Pure reference material and reference methods for HbA1c have been under development for many years by the International Federation of Clinical Chemistry (IFCC) (5) and are now in the final stages (6). From a clinical point of view, it is essential that HbA1c test results can be traced to the DCCT/UKPDS results where the relationships to risk for vascular complications have been established. Several experts have recommended that HbA1c should be reported in “DCCT-equivalent” percentage units (7,8) in order to avoid the confusion of adding another scale of numbers. We evaluated the effect on a diabetic patient population of raising the reference scale up to the DCCT level in 1992 and then down to the Swedish national standard in 1997. All patients at our center who had …