Objective: To evaluate the incidence and relative risk of type 2 diabetes defined by the newly proposed HbA(1c) diagnostic criteria in groups categorized by different baseline HbA(1c) levels.
Research design and methods: Using data from the European Prospective Investigation of Cancer (EPIC)-Norfolk cohort with repeat HbA(1c) measurements, we estimated the prevalence of known and previously undiagnosed diabetes at baseline (baseline HbA(1c) ≥6.5%) and the incidence of diabetes over 3 years. We also examined the incidence and corresponding odds ratios (ORs) by different levels of baseline HbA(1c). Incident diabetes was defined clinically (self-report at follow-up, prescribed diabetes medication, or inclusion on a diabetes register) or biochemically (HbA(1c) ≥6.5% at the second health assessment), or both.
Results: The overall prevalence of diabetes was 4.7%; 41% of prevalent cases were previously undiagnosed. Among 5,735 participants without diabetes at baseline (identified clinically or using HbA(1c) criteria, or both), 72 developed diabetes over 3 years (1.3% [95% CI 1.0-1.5]), of which 49% were identified using the HbA(1c) criteria. In 6% of the total population, the baseline HbA(1c) was 6.0-6.4%; 36% of incident cases arose in this group. The incidence of diabetes in this group was 15 times higher than in those with a baseline HbA(1c) of <5.0% (OR 15.5 [95% CI 7.2-33.3]).
Conclusions: The cumulative incidence of diabetes defined using a newly proposed HbA(1c) threshold in this middle-aged British cohort was 1.3% over 3 years. Targeting interventions to individuals with an HbA(1c) of 6.0-6.4% might represent a feasible preventive strategy, although complementary population-based preventive strategies are also needed to reduce the growing burden of diabetes.