Fasting plasma glucose and HbA1c as risk factors for Type 2 diabetes

Aims We examined the value of combining fasting plasma glucose (FPG) and glycated haemoglobin (HbA(1c)) as a predictor of diabetes, using the new American Diabetes Association (ADA) criteria of FPG and lower cut-off point of HbA(1c). Methods A retrospective cohort study was conducted from 1998 to 2006, inclusive, in 10 042 persons (55 884 person-years), with a mean age of 53.0 years at baseline. The cumulative incidence of diabetes (defined either as an FPG >= 7.0 mmol/l or as clinically diagnosed diabetes) was measured. Results The cumulative incidence and incidence density of diabetes were 3.7% (368 cases) and 6.6/1000 person-years over a mean follow-up period of 5.5 years. The cumulative incidence of diabetes in subjects with impaired fasting glucose (IFG) and HbA(1c) 5.5-6.4% was 24.8% (172/694 persons) compared with 0.4% (25/6698 persons), 2.5% (15/605 persons), 7.6% (156/2045 persons) in those with normal fasting glucose (NFG) and HbA(1c) < 5.5%, NFG and HbA(1c) 5.5-6.4% and IFG and HbA(1c) < 5.5%, respectively. The hazard ratio for diabetes, adjusted for possible confounders, was 7.4 (95% confidence interval, 4.70 to 11.74) for those with NFG and HbA(1c) 5.5-6.4%, 14.4 (11.93 to 27.79) for those with IFG and HbA(1c) < 5.5% and 38.4 (24.63 to 59.88) for those with IFG and HbA(1c) 5.5-6.4%. Conclusions The combination of FPG and HbA(1c) identifies individuals who are at risk of progression to Type 2 diabetes at the new ADA criteria of FPG and a lower cut-off point of HbA(1c) than previous studies.