We appreciate the interest of M.B. Davidson(1) in our study on the use of GHb as a screening test for diabetes(2). We agree with the author's contention that “diagnosis of diabetes is untenable in a person with a normal HbAlc level,” because these individuals are not at significant risk for development and/or progression of diabetic complications. It is important to note, however, that GHb can only be a reliable indicator of outcome risks, and therefore a useful alternative to fasting plasma glucose or oral glucose tolerance testing for diabetes screening, if GHb results are directly traceable to those of the Diabetes Control and Complications Trial(DCCT) and the U.K. Prospective Diabetes Study (UKPDS), where relationships to outcome risks have been established(3,4).
As noted in our report, the American Diabetes Association Expert Committee on the Diagnosis and Classification of Diabetes Mellitus did not recommend the use of GHb for diabetes screening or diagnosis in 1997, mainly because of the“many different methods for the measurement of GHb,” and because“nationwide standardization of the GHb test had just begun”(5). However, the National Glycohemoglobin Standardization Program (NGSP), initiated in 1996, has been highly successful in certifying GHb assay methods as traceable to the DCCT/UKPDS reference (6). Most GHb assay methods currently in use are NGSP-certified, and recent College of American Pathologists survey data show substantial improvement in the comparability of GHb results between various methods(7).