Japanese standard reference material for JDS Lot 2 haemoglobin A1c. I: comparison of Japan Diabetes Society-assigned values to those obtained by the Japanese and USA domestic standardization programmes and by the International Federation of Clinical Chemistry reference laboratories

Background: The Committee on Standardization of Laboratory Testing Related to Diabetes Mellitus of the Japan Diabetes Society (JDS) previously recommended use of the primary calibrator (JDS Lot 1) prepared by the former Committee for Standardization of Glycohemoglobin for standardizing the measurement of haemoglobin A1c (HbA1c). Owing to the depletion of vials of Lot 1 in March 2001, the present committee certified a new reference material, Lot 2, now distributed by the Health Care Technology Foundation (HECTEF). The standardization programme for HbA1c measurement in Japan is currently based on Lot 2, which has values assigned from within Lot 1; the Lot 1 values were consensus values based on assays by laboratories in the Japanese national quality control programme. In this study, for the purpose of international comparison and standardization, Lot 2 was assayed by the JDS reference laboratories, the National Glycoprotein Standardization Program (NGSP) in the USA, and by reference laboratories approved by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). Method: The HbA1c values of JDS Lot 2 were transferred from those assigned to Lot 1 using KO500, a high-resolution HPLC method, at three laboratories approved by the JDS committee. Subsequently, vials of JDS Lot 2 were shipped to and assayed by the NGSP in the USA and 10 IFCC reference laboratories. Result: The JDS-assigned HbA1c values (from Lot 1) are 4.04 for Level 1, 5.38 for Level 2, 7.32 for Level 3, 9.88 for Level 4, and 12.63 for Level 5, all expressed as a percentage of total haemoglobin. The values obtained by NGSP and the IFCC laboratories gave the following formulas: NGSP value (%) = JDS value (%) + 0.3%; IFCC value (%) = 1.068 x JDS value (%) -1.741%. Conclusion: Although the values obtained by the IFCC laboratories are significantly lower than the values assigned to Lot 2 by the JDS, the relationship is linear. In addition, standardization of HbA1c based on JDS Lot 2 is currently at a satisfactory level in Japan. As a result, the reassignment of values for Lot 2 to agree with the IFCC values should be relatively easy and will be done after all relevant parties agree to the change.