Prevalence and risks of hyperglycaemia and undiagnosed diabetes in patients with acute myocardial infarction.

Two studies were undertaken to assess the prevalence of undiagnosed diabetes mellitus in patients admitted with acute myocardial infarction (AMI), and the effect of diabetes mellitus and admission hyperglycaemia on outcome. In the retrospective study, admission levels of plasma glucose (APG) were higher (p less than 0.02) in patients dying from cardiogenic shock than in survivors, but they were not related to infarct size. In the prospective study APG was related (p less than 0.01) to concurrent levels of glycosylated haemoglobin (HbA1c), which were in turn related to outcome--the mortality rate was 23% for those with normal HbA1c (less than 7.5%), 33% for those with borderline abnormal HbA1c (7.5-8.5%), and 63% for those with clearly abnormal HbA1c (greater than 8.5%). Cardiogenic shock was commoner in the groups with higher HbA1c levels. In addition, admission hyperglycaemia was associated (p less than 0.01) with the incidence of cardiogenic shock even after correcting for the effects of HbA1c. All of the survivors from the clearly abnormal HbA1c group, but none of those from other groups, were diabetic at follow up, suggesting an overall prevalence of undiagnosed diabetes mellitus of 5.3%. The contribution of undiagnosed diabetes mellitus to total mortality following AMI seems at present to be underestimated.