Glycohaemoglobin: a crucial measurement in modern diabetes management - Progress towards standardisation and improved precision of measurement

There are currently four principal glycohaemoglobin assay techniques (ion-exchange chromatography, electrophoresis, affinity chromatography and immunoassay) and about 20 different methods that measure different glycated products and report different units. Standardisation will lead to all assays reporting results in a standard unit, the HbA(1c) percentage of total serum haemoglobin, and should be in place within the next one to three years. In the interim, clinicians using glycohaemoglobin assays should be aware that the ranges indicating good and poor glycaemic control can vary markedly between different assays. The reproducibility of some assays may be insufficient to provide definitive evidence of changes in glycaemic control. Some assays may be so imprecise that they are unable to separate patients with good and poor control. Interim recommendations 1 The terminology to be used for the assay is glycohaemoglobin (GHb) assay (recommendation from the combined meetings of the International Federation of Clinical Chemistry [IFCC] Working Group on HbA(1c) standardisation and the American Association of Clinical Chemistry [AACC] Subcommittee on Glycohemoglobin). 2 The unit of measurement for GHb assays should be reported as %HbA(1c) (Diabetes Control and Complications Trial equivalent). 3 Other units, such as % total GHb or %HbA1, should not be used. Assays producing these units should be converted to %HbA(1c) reporting units. 4 Assays with high precision are highly desirable. The IFCC/AACC are currently recommending between-run coefficients of variation of less than 5% for manufacturers of kits and instruments. However, between-run coefficients of variation of less than 3% are far more clinically useful and therefore desirable.