Interlaboratory comparison of glycohemoglobin results: College of American Pathologists Survey data

We describe recent changes in the College of American Pathologists Glycohemoglobin (gHb) Survey, made to improve the assessment of interlaboratory variability and the accuracy of results reported. The questionnaire portion of the survey was revised to include an updated list of current methods, and results for survey specimens were grouped according to the component measured (Hb A1, Hb A1c, or total gHb). The survey specimen material was changed to a material thought to give more reliable results with all available methods. After these changes, instituted in 1989, between-laboratory CVs decreased for some methods. Furthermore, gHb values between method types were more consistent with results obtained from fresh blood samples under very controlled laboratory conditions. However, these recent data also show that the interlaboratory variability is still quite high for some methods and that the variability within and between method types is still very great. We describe a pilot standardization program for gHb measurement.