The utility of fasting plasma glucose in predicting glycosylated hemoglobin in type 2 diabetes

BACKGROUND: Access to glycosylated hemoglobin (HbA1c) assays in clinical practice remains limited. We investigated the relationship of fasting plasma glucose and HbA1c to determine optimal glucose levels for predicting HbA1c. PATIENTS AND METHODS: We retrospectively analyzed data on 2888 patients with type 2 diabetes mellitus aged ≥20 years using a linear regression of HbA1c against fasting plasma glucose. A receiver-operating characteristic analysis was used to determine optimal cut-points for fasting glucose in relation to HbA1c, area under the curve, sensitivity and specificity, and 95% confidence intervals (CI) for each cut-point. RESULTS: The mean (standard deviation) for the age of patients was 52±11.6 years. The average HbA1c was 8.9±2.46% and mean fasting plasma glucose was 10.1±3.62 mmol/L. The prevalence of HbA1c ≥7.0% and >6.5% was 76% and 82%, respectively. Overall, fasting plasma glucose and HbA1c were linearly correlated (r=0.62, P=0.001). A fasting plasma glucose of >9.0 mmol/L predicted HbA1c ≥7.0% with an area under the curve = 0.807 (95% CI, 0. 0.794 to 0.821), while fasting plasma glucose >8.2 mmol/L predicted HbA1c >6.5%, with an area under the curve = 0.805 (95% CI, 0.791 to 0.818). The sensitivity of both cut-points was 64.5% and 70.7%, the specificity was 82.7% and 76.4%, the positive likelihood ratio was 3.73 and 2.99, and the positive predictive value was 92.2% and 93.2%, respectively. CONCLUSION: When HbA1c determination is not available, fasting plasma glucose levels may be used to identify patients with uncontrolled type 2 diabetes and initiate timely intensification of therapy to avoid long-term complications of diabetes.