Hyperglycaemia following acute myocardial infarction: the contribution of undiagnosed diabetes.

We studied 397 patients admitted to hospital with acute myocardial infarction (AMI) to validate an admission level of haemoglobin A1c (HbA1c) diagnostic for previously unknown diabetes mellitus by assessing glucose tolerance after 3 months. In 38% of survivors clearly abnormal HbA1c level (greater than 7.8) was 100% sensitive and 99% specific for diabetes with fasting hyperglycaemia, although the sensitivity fell to 67% when three diabetic subjects without fasting hyperglycaemia were included. Admission hyperglycaemia (plasma glucose greater than or equal to 11 mmol/l) was present in 20% of patients with AMI, of whom only one in five had levels of HbA1c indicating prior diabetes. Glycosylated haemoglobin is a more sensitive and specific test for diabetes in patients with AMI than admission hyperglycaemia. Undiagnosed diabetes was found in 4.3% of subjects with AMI who contributed 9.6% of hospital mortality.