HbA1c as a screening tool for detection of Type 2 diabetes:: a systematic review

Aim To assess the validity of glycated haemoglobin A(1c) (HbA(1c)) as a screening tool for early detection of Type 2 diabetes. Methods Systematic review of primary cross-sectional studies of the accuracy of HbA(1c) 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, HbA(1c) has slightly lower sensitivity than fasting plasma glucose (FPG) in detecting diabetes, but slightly higher specificity. For HbA(1c) 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 HbA(1c) and FPG have low sensitivity for the detection of impaired glucose tolerance (around 50%). Conclusions HbA(1c) and FPG are equally effective screening tools for the detection of Type 2 diabetes. The HbA(1c) cut-off point of > 6.1% was the recommended optimum cut-off point for HbA(1c) 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 HbA(1c) has less intra-individual variation and better predicts both micro- and macrovascular complications. Although the current cost of HbA(1c) is higher than FPG, the additional benefits in predicting costly preventable clinical complications may make this a cost-effective choice.