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

Introduction American Diabetes Association (ADA) has officially endorsed glycosylated haemoglobin (HbA_1c) as a diagnostic tool. The recommended cut-off for diagnosing diabetes is ≥6.5%.

Objectives To compare use of HbA_1c 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. HbA_1c was measured by National Glycohaemoglobin Standardization Program certified Bio Rad Variant HbA_1c HPLC method. Diagnostic performance of HbA_1c was evaluated in those without previous diabetes. Receiver Operating Characteristic Curve was used to identify optimum HbA_1c 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%). HbA_1c was ≥6.5% in 173(6.9%). Concordance between FPG and HbA_1c was 95% (both criteria positive: 5.8%; both criteria negative: 89.2%). Compared to FPG, HbA_1c 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 HbA_1c 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 HbA_1c criterion was 29% less than with FPG criterion.  Compared to FPG, HbA_1c had high specificity but sensitivity was low. Further research is needed to refine the optimum HbA_1c threshold in Sri Lankans.