Standardization of HbA1c value and its comparison to immunoassay — two years of experience

Abstract In spite of the routine use of hemoglobin A1c (HbA1c) value to guide diabetes therapy, substantial differences have been noted between results obtained by different instruments and laboratories. It was suggested that confusion between the terms used for HbA1c, i.e. between ‘total HbA1c’, which includes labile content, and ‘stable HbA1c’, which does not, may account for some of these inter-instrument and inter-laboratory differences. However, an undesirable difference was found even in measurements of only the stable component of HbA1c using the two most commonly used HPLC analyzers in our country. We found that a two-point calibration using lyophilized hemoglobin at lower and higher ranges was effective in matching up results of HbA1c measurement. This finding was concordant with a report by the Committee of the Japan Diabetes Society and other reports. Two methods of HbA1c immunoassay, one performed with the DCA 2000 automated analyzer and another performed using the Liquitech kit or a general automated analyzer, were evaluated and found to perform as well as HPLC analyzers in all respects except precision. The results derived from immunoassay were in good agreement with the calibrated results by HPLC, with (Liquitech) and without (DCA 2000) conversions.