Survey and assessment of the actual state of routine measurement of glycohaemoglobin/GHb by commercial methods: warning to the users and the providers.

As the clinical availability of glycohaemoglobin/GHb measurement increases, so does the need for comparable and accurate values among different laboratories and different methods. At least there should be comparability, i.e., commutability or feasibility of providing comparable results from different assays in different laboratories. A clinical joint study on insulin therapy, a survey of the actual inter-laboratory differences in GHb measurement among 41 institutions and an assessment of 11 assay methods for the determination of GHb were performed using commercial calibrators and fresh blood samples. Data on the actual state of inter-laboratory and inter-assay differences of observed values were useful for comparing results among facilities. The recommendation of the Japan Diabetes Society to measure only the stable GHb component and to correct the GHb percentage by two-point calibration with assigned values, was effective but not sufficient. Even after correction, 8 out of 11 methods still remained of little practical use because of their large relative errors. Inter-method differences among 11 available assay methods were great even after correction and depended on not only the methods but the samples used for the determination. The performance of some methods or instruments used are only poor at distinguishing the stable glycated haemoglobin itself. Some alternative measurement system with comparability, commutability and precision should be established. An urgent and worldwide problem to remove inter-laboratory differences in the measurement of GHb needs to be solved. Users in clinical practice must recognize these problems, and, before supply, the providers should check their method and keep records that are readily traceable.