[The worldwide standardization of hemoglobin A1c measurement: the current statement from the Japan Diabetes Society and the issues to be solved].

Abstract The American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) have recently decided to use both units in the hemoglobin A1c (HbA1c) measurement based on the NGSP (previously called the National Glycohemoglobin Standardization Program) and the IFCC (International Federation of Clinical Chemistry) in articles and scientific meetings, whereas each country or region may use either NGSP units (conventional %) or IFCC units (SI; mmol/mol) in common practice. This is expressed as "a new twist on the path to harmony" in the measurement of HbA1c. Accordingly, the Japan Diabetes Society has used only NGSP units as of April 1, 2013, whereas the previous JDS units will be used for the high reproducibility of the JDS Standardization System but not in the clinical setting. JDS units are converted to NGSP units using JDS lots in Japan. Unfortunately however, there are significant differences between NGSP values obtained by the previously reported IFCC-JDS equations and those currently available in Japan. Therefore, this paper argues that IFCC units as the only valid anchor for scientific standardization should seek robust master equations for NGSP and JDS units. Furthermore, the biological variability of HbAlc, such as the Hemoglobin Glycation Index and the Glycation Gap, may be accurately evaluated by IFCC units because the values do not include additional factors such as non-glycated Hb in JDS and NGSP units.