Utility of glycosylated haemoglobin in diagnosing diabetes in an urban Sri Lankan community

Introduction American Diabetes Association (ADA) has officially endorsed glycosylated haemoglobin (HbA1c) as a diagnostic tool. The recommended cut-off for diagnosing diabetes is  6.5%. Objectives To compare use of HbA1c and fasting plasma glucose (FPG) to diagnose diabetes in an urban Sri Lankan community. Methods This cross-sectional study is based on baseline data from a prospective study on non-communicable diseases in randomly selected individuals aged 35-64 years in a selected community. HbA1c was measured by National Glycohaemoglobin Standardization Program certified Bio Rad Variant HbA1c HPLC method. Diagnostic performance of HbA1c was evaluated in those without previous diabetes. Receiver Operating Characteristic Curve was used to identify optimum HbA1c threshold. Results We studied 2516 individuals with no previous history of diabetes. Of these 53.8% were women. Mean age was 52 ± 7.9 years. FPG was 7mmol/l in 245 (9.7%). HbA1c was  6.5% in 173 (6.9%). Concordance between FPG and HbA1c was 95% (both criteria positive: 5.8%; both criteria negative: 89.2%). Compared to FPG, HbA1c cut-off of 6.5% had specificity of 98.9% (95% CI 98.3-99.3) and sensitivity of 60% (95% CI 53.6-66.2). Positive and negative predictive values were 85% (95% CI 78.8-89.9) and 95.8% (95% CI 94.9-96.6), respectively. Compared to FPG, optimum HbA1c threshold for diagnosing diabetes was 5.9% (sensitivity: 84%; specificity: 88.8%; area under the curve: 0.91). Conclusions In the study population, detection of diabetes with ADA recommended HbA1ccriterion was 29% less than with FPG criterion. Compared to FPG, HbA1c had high specificity but sensitivity was low. Further research is needed to refine the optimum HbA1c threshold in Sri Lankans.