Proficiency testing of Hb A_1c: A 4-year experience in Taiwan and the Asian Pacific region

BACKGROUND: The correlation between hemoglobin A_1c (Hb A _1c) and risk for complications in diabetic patients heightens the need to measure Hb A_1c with accuracy. We evaluated the current performance for measuring Hb A_1c in the Asian and Pacific region by examining data submitted by laboratories participating in the Taiwan proficiency-testing program. METHODS: Five fresh-pooled blood samples were sent to participating laboratories twice each year. The results were evaluated against target values assigned by the National Glycohemoglobin Standardization Program network laboratories; a passing criterion of ±7% of the target value was used. Measurement uncertainty at Hb A_1c concentrations of 7.0% and 8.0% were determined. RESULTS: A total of 276 laboratories from 11 countries took part in the Hb A_1c survey. At the Hb A_1c concentrations tested method-specific interlaboratory imprecision (CVs) were 1.1%-13.9% in 2005, 1.3%-10.1% in 2006, 1.2%-8.2% in 2007, and 1.1%-6.1% in 2008. Differences between target values and median values from the commonly used methods ranged from -0.24% to 0.22% Hb A_1c in 2008. In 2005 83% of laboratories passed the survey, and in 2008 93% passed. At 7.0% Hb A _1c,measurement uncertainty was on average 0.49% Hb A_1c. CONCLUSIONS: The use of accuracy-based proficiency testing with stringent quality criteria has improved the performance of Hb A_1c testing in the Asian and Pacific laboratories during the 4 years of assessment.