Using haemoglobin A1c to diagnose type 2 diabetes or to identify people at high risk of diabetes

#### Learning points A 48 year old man presented to his general practitioner with a 12 month history of fatigue (which he put down to long office hours) and with urinary frequency. He had no previous health problems, his blood pressure was 145/85 mm Hg, and his body mass index was 29. His father had developed type 2 diabetes at the age of 65 years, and his paternal grandmother had been found to have diabetes at the age of about 60 following the development of a gangrenous toe. The patient’s dipstick urine test showed no glycosuria, ketonuria, proteinuria, blood, leucocytes, or nitrites. All the possible causes of fatigue should be considered,1 but given the patient’s symptoms and his risk factors for developing type 2 diabetes, including family history and being overweight, a diagnosis of diabetes certainly needs to be excluded. Tests for diabetes are used to evaluate both patients with symptoms (as in this case) and asymptomatic patients who have been identified by a validated risk assessment tool as being at high risk of developing type 2 diabetes.2 Since the early 20th century, the diagnosis of diabetes has been based on the measurement of glucose concentrations in the blood. This usually takes the form of laboratory measured fasting plasma glucose concentration and, when indicated, …