The potential impact and optimal cut-points of using glycated haemoglobin, HbA1c, to detect people with impaired glucose regulation in a UK multi-ethnic cohort

IntroductionRecommended diagnostic cut-points to detect impaired glucose regulation (IGR, also termed prediabetes: impaired fasting glucose and/or impaired glucose tolerance based on WHO 1999 criteria) are HbA1c 6.0–6.4% and 5.7–6.4% from an International Expert Committee and American Diabetes Association, respectively. We investigated the impact on prevalence/phenotype from using these criteria compared to IGR detected on oral glucose tolerance testing (OGTT) and determined optimal HbA1c cut-points for IGR in a multi-ethnic cohort.MethodsAnalysis of 8696 participants in the LEADER study of primary care individuals aged 40–75 years without diabetes, in Leicestershire (UK) who underwent OGTT and had HbA1c measured.ResultsUse of OGTT detected less people with IGR (n = 1407, 16.2%) compared to HbA1c 6.0–6.4% (n = 1610, 18.5%) and HbA1c 5.7–6.4%(n = 3904, 44.9%), a 1.1- and 2.8-fold increase in prevalence, respectively. There were 930 (10.7%) and 534 (6.1%) people with IGR on OGTT not detected using HbA1c 6.0–6.4% and 5.7–6.4%, respectively. From ROC curve analysis, the optimal cut-point for detecting IGR in white Europeans was HbA1c ≥ 5.8%, sensitivity/specificity 61.5%/67.9%, but in south Asians HbA1c ≥ 6.0%, sensitivity/specificity 63.8%/69.4%.ConclusionRecommended HbA1c cut-points to detect IGR significantly increase numbers detected, however introduce a change in people identified. Using HbA1c 6.0–6.4% lacks sensitivity in white Europeans, but is a reasonable option in south Asians.