Oral glucose tolerance test as a prognostic tool in patients with acute coronary syndrome

Abstract

Background: Disturbances of glucose metabolism such as type 2 diabetes and impaired glucose tolerance are established risk factors for cardiovascular disease and mortality. The disturbances lead to hyperglycaemia and the most common methods to diagnose hyperglycaemia are HbA1c, oral glucose tolerance test (OGTT) and fasting plasma glucose (FPG). The best method to predict death and cardiovascular disease is still being debated.

Aims: 1. To assess cardiovascular outcome a decade after acute coronary syndrome (ACS) and its relationship with repeated measurements of metabolic status and indices of glycaemic abnormalities; 2. To study long-term prognosis in patients with acute myocardial infarction and glucose abnormalities and focus on the predictive value of an oral glucose tolerance test and HbA1c; 3. To study preoperative disturbances of glucose metabolism and mortality after coronary artery bypass grafting (CABG); and 4. To study the prognostic importance of random prandial blood glucose tests and the risk of mortality and cardiovascular events in patients attending the Emergency Department (ED).

Methods: In studies I-III all participants without known diabetes underwent a 75-g OGTT according to the World Health Organization (WHO) and were divided into different glucose tolerance groups depending on the result of the OGTT. In studies I-II, the OGTT was performed 4-5 days after the study population had been treated for myocardial infarction. In paper III, the OGTT was performed within 3 months of a CABG. In study IV, the study population had a random blood glucose test taken upon admission to the ED.

Results: In Study I, the revaluation of the metabolic status in 515 patients was done after 4 years and the mortality and cardiovascular events were studied after a decade. Patients with known diabetes type 1 and type 2 had higher mortality and incidence of cardiovascular events compared to the patients without diabetes, and patients with prediabetes had a higher incidence of cardiovascular events compared to patients with diabetes diagnosed by OGTT. At 4-years follow-up, the indices of metabolic control were higher in patients with dysglycaemia than in patients with normal glucose tolerance (NGT). In Study II, 754 patients out of 1684 treated for acute myocardial infarction had an HbA1c and an OGTT controlled at the time of their infarction and were diagnosed with dysglycaemia using either OGTT or HbA1c. HbA1c in the prediabetes range, but not OGTT, added predictive value on the long-term outcome. In Study III, 497 patients were studied regarding their outcome in accordance with their glucose tolerance group after CABG. There was no significant difference in all-cause mortality between patients with diabetes, prediabetes or NGT during a mean follow-up time of 10 years. In Study IV, 662,018 patients had a random plasma glucose test when attending the ED. Patients with newly discovered diabetes had approximately a 2-fold risk of all-cause mortality compared to patients with normal glucose tolerance at 3.9 years follow-up.

Conclusion: A majority of patients with cardiovascular events have undiagnosed disturbances of glucose tolerance and the long-term outcome in those patients is poorer compared to patients with NGT. HbA1c may be a better predictor than OGTT to identify patients at risk for premature death and cardiovascular events. Elevated plasma glucose test taken in the ED, can predict premature death.