IFCC standardised HbA_1c: should the world be as one?

Abstract

The central importance of HbA_1c in monitoring glycaemic control was highlighted by the Diabetes Control and Complications Trial (DCCT) which showed that improved glycaemic control, as monitored by HbA_1c, delayed the onset of diabetic complications. Following this publication the issue of international standardisation of glycated haemoglobin (GHb) measurements became an important objective. The lack of international standardisation resulted in several countries developing National Standardisation Programmes. The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Working Group on HbA_1cStandardisation has established a reference measurement procedure (HPLC-MS or HPLC-CE) for HbA_1c embracing the concept of metrological traceability. The reference method is anchored to a global network of 15 approved reference laboratories; this confers sustainability and a low level of uncertainty. Essential elements of a comprehensive reference measurement system additionally include the definition of the measurand and the unit of measurement. HbA_1c is defined as haemoglobin (Hb) molecules having a stable adduct of glucose to the N-terminal valine of the β chain [Hb β chain (Blood) – N-(1-deoxyfructos-1-yl) Hb β chain] and that mmol/mol be used as the unit of measurement. These developments will result in improvements in inter-method and inter-laboratory agreement. Additionally, global acceptance of standardisation based on metrologically sound principles will enable clinical goals and diagnostic guidelines to be developed that can be adopted by all countries.