Aim: To assess the validity of glycated haemoglobin A1c (HbA1c) as a screening tool for early detection of Type 2 diabetes.
Methods: Systematic review of primary cross-sectional studies of the accuracy of HbA1c for the detection of Type 2 diabetes using the oral glucose tolerance test as the reference standard and fasting plasma glucose as a comparison.
Results: Nine studies met the inclusion criteria. At certain cut-off points, HbA1c has slightly lower sensitivity than fasting plasma glucose (FPG) in detecting diabetes, but slightly higher specificity. For HbA1c at a Diabetes Control and Complications Trial and UK Prospective Diabetes Study comparable cut-off point of ≥ 6.1%, the sensitivity ranged from 78 to 81% and specificity 79 to 84%. For FPG at a cut-off point of ≥ 6.1 mmol/l, the sensitivity ranged from 48 to 64% and specificity from 94 to 98%. Both HbA1c and FPG have low sensitivity for the detection of impaired glucose tolerance (around 50%).
Conclusions: HbA1c and FPG are equally effective screening tools for the detection of Type 2 diabetes. The HbA1c cut-off point of > 6.1% was the recommended optimum cut-off point for HbA1c in most reviewed studies; however, there is an argument for population-specific cut-off points as optimum cut-offs vary by ethnic group, age, gender and population prevalence of diabetes. Previous studies have demonstrated that HbA1c has less intra-individual variation and better predicts both micro- and macrovascular complications. Although the current cost of HbA1c is higher than FPG, the additional benefits in predicting costly preventable clinical complications may make this a cost-effective choice.