Evidence of the Month

1. Evidence of the Month Consensus statement on the worldwide standardization of the hemoglobin A1C measurement: the American Diabetes Association, European Association for the Study of Diabetes, International Federation of Clinical Chemistry and Laboratory Medicine, and the International Diabetes Federation. Diabetes Care. 2007;30:2399-2400. Consensus statement on the worldwide standardisation of the HbA1c measurement: the American Diabetes Association, European Association for the Study of Diabetes, International Federation of Clinical Chemistry and Laboratory Medicine, and the International Diabetes Federation. Diabetologia. 2007;50:2042-2043.

2. Overview In 2007, the same consensus statement on the worldwide standardisation of HbA1c was published in Diabetes Care and Diabetologia Consensus statement was created by American Diabetes Association, European Association for the Study of Diabetes, International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), and International Diabetes Federation Recommended that HbA1c be reported as 3 different values mmol/mol (IFCC units) % (derived NGSP units using the IFCC-NGSP master equation) If ongoing average plasma glucose study fulfils its a priori criteria, then an HbA1c-derived average glucose, or estimated average glucose, calculated from the HbA1c will also be reported

3. Existing HbA1c measurement Currently, HbA1c largely reported in NGSP (or DCCT) units Results comparable to values obtained by patients in DCCT and UKPDS Clinicians and patients familiar with the values BUT Not �true� HbA1c values but closest possible using 1980s technology Values therefore currently �harmonised� to DCCT rather than traceable to a true standard

4. Clinical implications of new HbA1c measurement For greater accuracy, IFCC developed a reference method for HbA1c These values are 1.5 % to 2 % HbA1c lower than currentHbA1c values However, may lead to confusion between these and existing DCCT numbers This concern led to suggestion of expressing HbA1c as mean plasma glucose equivalent (also called estimated average glucose [eAG]) Patients may be better able to equate this result to that obtained from meter readings However, still has to be shown that HbA1c accurately reflects mean blood glucose in most situations To avoid confusion with DCCT values, IFCC proposed using mmol/mol where, for example, 7 % HbA1c=70 mmol/mol

5. Clinical implications of new HbA1c measurement In relation to eAG, could be argued that the criteria to accept as a replacement for HbA1c are not sufficiently robust Consequently, one patient could have a true mean glucose considerably higher than another yet both have the same eAG Study results will need to ensure that eAG not adopted to the detriment of these types of patients eAG value will not be uniform as results will vary depending on whether glucose is expressed as mmol/l or mg/dl Great upheaval likely in any switch to mmol/mol units due to lack of familiarity with these units Also problematic in countries that express glucose as mg/dl Will need to educate health care workers in what values mean Likely that reporting of 3 numbers will lead to re-evaluation of new consensus, with the possibility that there will be less rather than more global harmonisation