For many years, the diagnosis of diabetes has been made through the laboratory-based measurement of fasting or random blood glucose levels, or using the oral glucose tolerance test. A glycated haemoglobin (HbA(1c)) level ≥ 6.5% (48 mmol/mol) is now also acceptable for diagnosing diabetes. Caution is needed in interpreting HbA(1c) test results in the presence of conditions affecting red blood cells or their survival time, such as haemoglobinopathies or anaemia.