HbA1c standardization: Background, progress and current issues

Abstract

HbA1c is used to monitor glycemic control in diabetic patients with specific HbA1c treatment goals. The National Glycohemoglobin Standardization Program (NGSP) was developed to standardize HbA1c to clinical data from the Diabetes Control and Complications Trial (DCCT). The NGSP has a certification program for manufacturers and laboratories as well as ongoing monitoring of the quality of HbA1c measurements; the program has been successful in reducing variability among laboratories. Standardization programs in Japan and Sweden were also developed. All 3 programs used designated comparison methods and not "true" reference methods. The International Federation of Clinical Chemistry (IFCC) Working Group on HbA 1c standardization subsequently developed a reference measurement system based on the concepts of metrological traceability. NGSP and IFCC HbA1c results are highly correlated but report different numbers. A consensus statement of 3 major clinical organizations and the IFCC has recommended reporting of the current NGSP numbers (%), the new IFCC numbers (mmol/mol), and estimated average glucose.