Haemoglobin A1c (HbA1c) or glycohaemoglobin is one of the most important parameters in the management of patients with diabetes mellitus, but to date there is no international standard for determining HbA1c. Most of the routine HbA1c assays are standardised against one of the local standardisation schemes like the NGSP (USA) and other schemes (Japan, Sweden). Still, results of HbA1c tests diverge considerably, as do the accompanying clinical decision limits.
The IFCC Working Group on HbA1c Standardisation has developed a reference method and also set up a reference system for HbA1c, in which the analyte is defined as β-N-glycated haemoglobin. This reference system consists of a network of reference laboratories that uses the reference methods and certified reference materials for optimal measurement of HbA1c in human blood. The main task of the network is to assign values to secondary reference materials, to be used by manufacturers of routine HbA1c assays to calibrate their assays. The high specificity of the reference method results in lower HbA1c values in blood samples, since the unspecific components falsely identified as HbA1c in routine methods are not measured by the reference method. The reference range for the new reference method was determined as 3 to 4% and the clinical decision limits were translated from existing guidelines: goal of treatment 5% HbA1c, change of therapy advised at HbA1c greater than 6%. Despite these lower values, worldwide implementation of the IFCC reference system for HbA1c is recommended, in order to end the great divergence in HbA1c results, with which physicians and patients are confronted today.