The general use of glycated haemoglobin for the diagnosis of diabetes and other categories of glucose intolerance: still a long way to go

Glycated haemoglobin (HbA_1c) is considered the ‘gold standard’ for monitoring metabolic control in diabetes. An International Expert Committee recently recommended HbA_1c as a better method than measurement of glucose to use in the diagnosis of diabetes, based on its strong association with microvascular complications, a lower day-to-day variability and ease of use, not necessarily in the fasting state. These recommendations have been embraced by the American Diabetes Association (ADA), which stated in its Standards of Medical Care in Diabetes 2010 that “A_1c, fasting plasma glucose or the 2 h 75 g oral glucose tolerance test (OGTT) are appropriate for testing diabetes and assessing the risk of future diabetes,” and that “a confirmed A_1c ≥ 6.5% is diagnostic for diabetes.” Measuring HbA_1c has several advantages over glucose measurements, but its exclusive use should only be considered if the test is conducted under standardised conditions and its limitations are taken into due account. The impact of its use on the epidemiology of diabetes and other categories of glucose intolerance, as seen from recent reports, is also discussed.