Towards worldwide standardisation of HbA₁c determination

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.