Hemoglobin A1c in combination with fasting plasma glucose trumps fasting plasma glucose alone as predictive indicators for diabetes mellitus: an ambidirectional cohort study of Thai people with impaired fasting glucose

INTRODUCTION: This ambidirectional cohort study aimed to assess the performance of combining hemoglobin A1c (HbA1c) to fasting plasma glucose (FPG) for estimation of progression rate to diabetes mellitus (DM) and to explore the risk factors of DM in patients with impaired fasting glucose (IFG). RESEARCH DESIGN AND METHODS: Patients with IFG were eligible for this study. IFG was defined as FPG of 100–125 mg/dL. Progression rates to DM were estimated using Kaplan-Meier analysis. Risk factors of DM were explored by Cox regression analysis. RESULTS: 3011 patients were enrolled with median follow-up time of 8 years (range: 6 months–29 years). Progression rates to DM in patients with FPG 100–109 mg/dL and 110–125 mg/dL were 2.64 and 4.79 per 100 person-years. After adjusting covariables, compared with patients with FPG 100–109 mg/dL plus normal HbA1c (<5.7%), hazard ratios (95% CI) of patients with FPG 110–125 plus normal HbA1c, FBG 100–109 plus abnormal HbA1c (5.7%–6.49%), and FPG 110–125 plus abnormal HbA1c were 5.89 (2.37 to 14.63), 16.30 (8.59 to 30.92), and 33.84 (16.41 to 69.78), respectively. Body mass index ≥27.5 kg/m(2), serum triglyceride level ≥150 mg/dL, family history of DM, and low level of high-density lipoprotein-cholesterol were independently associated with risk of DM in patients with IFG. CONCLUSIONS: Patients with both IFG and abnormal HbA1c had higher risk of DM than patients with IFG alone. Therefore, performing HbA1c in combination with FPG helps to identify subgroups of people with IFG at highest risk of DM. These patients should have the highest priority in diabetes prevention programs, especially in countries with low and limited resources.