Predicting type 2 diabetes mellitus using haemoglobin A1c: a community-based historic cohort study.

BACKGROUND: The ADA 2010 guidelines added HbA1c ≥ 6.5% as a criterion for diagnosing diabetes mellitus type 2.

OBJECTIVE: To evaluate the HbA1c test in predicting type 2 diabetes in a high risk population.

METHODS: A community-based historic cohort study was conducted including 10 201 patients, who had not been diagnosed with diabetes, and who underwent HbA1c test during the years 2002-2005. Data was retrieved on diabetes risk factors and the onset of diabetes (according to the ADA 2003 criteria), during a follow-up period of five-to-eight years.

RESULTS: Mean age was 58.25 ± 15.58 years; mean HbA1c level was 5.59 ± 0.55% and 76.8% had a BMI > 25 kg/m(2) (mean: 30.74 ± 8.30). In a Cox proportional hazards regression model, the risk of developing type 2 diabetes was 2.49 (95% CI: 1.29-3.71) for 5.5% ≤ HbA1c < 6% at baseline, 4.82 (95% CI: 2.83-8.20) for 6% ≤ HbA1c < 6.5% at baseline and 7.57 (95% CI: 4.43-12.93) for 6.5% ≤ HbA1c < 7% at baseline, compared to HbA1c < 4.5%. The risk of developing diabetes was 1.14 (95% CI: 1.05-1.25) for male gender, 1.16 (95% CI: 1.04-1.28) for cardiovascular diseases and 2.06 (95% CI: 1.80-2.35) for overweight (BMI > 25 kg/m(2)) at baseline. Neither age nor low socio-economic status was associated with increased risk of diabetes.

CONCLUSION: Levels of HbA1c ≥ 5.5% were associated with increased risk of type 2 diabetes during a five-to-eight-year follow-up period. Findings support the use of HbA1c testing as a screening tool in populations at risk of developing diabetes.