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

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Abstract
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.