Role of proficiency testing in monitoring of standardization of hemoglobin A1c methods

After Hemoglobin A1c (HbA1c), therapeutic targets for monitoring diabetes therapy were recommended, first, National Glycohemoglobin Standardization Program (NGSP), then, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) developed standardization initiatives. The aim of this article is to demonstrate the role of a proficiency testing (PT) programs in monitoring the long-term effect of these initiatives and the current status of HbA1c measurement. Measurement precision as a coefficient of variation (CV), measurement bias (bias), and satisfactory HbA1c result rates in proficiency testing (PT) surveys were evaluated using fresh single donor whole blood PT items and assigned values from a NGSP-certified secondary reference laboratory. Between 2000 and 2010, both CV and bias of the IC measurement method showed a decreasing trend. While the CV of the HPLC measurement method decreased, no significant change was observed in its bias. The rates of satisfactory HbA1c results in PT surveys were higher in HPLC users than IC users. In 2010, the average CVs in HPLC and IC groups were 2.6 and 3.4 %, biases were 2.7 and 1.8 %, and corresponding total error (TE) estimates were 7.8 and 8.5 %, respectively. These TE values were higher than the maximum permissible measurement error of 7 %, developed based on clinical use of the test. The NGSP and the IFCC networks have promoted improvements in HbA1c testing; however, tightening of NGSP method certification criteria seems to be necessary to achieve a maximum permissible measurement error of 7 %.