HbA1c in diagnosing and predicting Type 2 diabetes in impaired glucose tolerance: the Finnish Diabetes Prevention Study

P>Aims We analysed the Finnish Diabetes Prevention Study data in order to evaluate how the new HbA(1c)-based criterion compares with the oral glucose tolerance test in diagnosing Type 2 diabetes among high-risk individuals during a prospective average follow-up of 4 years. Methods In the Diabetes Prevention Study, 172 men and 350 women who were overweight and had impaired glucose tolerance at baseline were randomized into an intensive lifestyle intervention or a control group. The oral glucose tolerance test and HbA(1c) measurements were performed annually until the diagnosis of diabetes using the World Health Organization 1985 criteria. Results The sensitivity of the HbA(1c)>= 6.5% (>= 48 mmol/mol) as a diagnostic criterion for Type 2 diabetes was 35% (95% CI 24%, 47%) in women and 47% (95% CI 31%, 64%) in men compared with diagnosis based on two consecutive oral glucose tolerance tests. The corresponding sensitivities for HbA(1c)>= 6.0% (>= 42 mmol/mol) were 67% (95% CI 55%, 77%) and 68% (95% CI 51%, 82%). The participants with HbA(1c)>= 6.5% (>= 48 mmol/mol) and diabetes based on the oral glucose tolerance test were more obese and had higher fasting glucose and 2-h glucose concentrations than those who had a diabetic oral glucose tolerance test but HbA(1c) < 6.5% (< 48 mmol/mol). There were no differences in the predictive performance of baseline fasting glucose, oral glucose tolerance test and HbA(1c). Conclusions Of those with diabetes diagnosis based on two oral glucose tolerance tests during the Diabetes Prevention Study follow-up, 60% would have remained undiagnosed if diagnosis had been based on HbA(1c)>= 6.5% (>= 48 mmol/mol) criterion.