The assay of glycated haemoglobin (HbA1c) is a gold standard in bioanalysis, and is essential to ensure the optimal care of diabetic patients. Accordingly, the principal scientific societies in diabetology and clinical chemistry have made efforts to standardize this assay in order to select and validate certain analytical methods and achieve consistency in the results obtained therewith. However, clinicians have to be aware of the caution required when interpreting HbA1c assay results owing to modified lifetime and (or) abnormal synthesis of haemoglobin. Although this biological examination has now become an essential part of diabetes monitoring, its status as a screening tool is still controversial, even after 30 years of debate. Other uses of HbA1c assay are currently being assessed in cardiology (coronary syndromes), vascular diseases (arteriopathy), nephrology (renal insufficiency), haematology (anaemia) and oncology (factors of predisposition).