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.

INTRODUCTION: Recommended 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.
METHODS: Analysis 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.
RESULTS: Use 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>or=5.8%, sensitivity/specificity 61.5%/67.9%, but in south Asians HbA1c>or=6.0%, sensitivity/specificity 63.8%/69.4%.
CONCLUSION: Recommended 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.