Abstract

The Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS) demonstrated conclusively that risks for complications in patients with diabetes are directly related to glycemic control, as measured by glycated hemoglobin (GHb). Many diabetes organizations worldwide now recommend GHb targets in terms of DCCT/UKPDS hemoglobin A_1c (HbA_1c). However, in 1993 there was a lack of comparability of GHb test results among methods and laboratories that represented a major obstacle to meaningful implementation of specific guidelines for diabetes care. The National Glycohemoglobin Standardization Program (NGSP) was implemented to enable laboratories to report DCCT/UKPDS-traceable GHb/HbA_1c results.

The number of methods and laboratories certified by the NGSP as traceable to the DCCT has steadily increased. Proficiency testing results show marked improvement in the comparability of GHb results. By the end of 2002, 98% of surveyed laboratories (n = approx. 2000) reported GHb results as HbA_1c or equivalent compared to 50% in 1993. Ninety-seven percent of laboratories used an NGSP-certified method. For most certified methods in 2002, between-laboratory CVs were <5%. For all certified methods in 2002, the mean HbA_1c value (%) was within 0.8% HbA_1c from the NGSP target at all HbA_1c concentrations. The vast majority of laboratories in the US are now reporting results that are traceable to DCCT/UKPDS outcomes.