Is glycated haemoglobin testing appropriate for screening and diagnosis of type 2 diabetes mellitus among Africans?

Introduction: Glycated Haemoglobin (HbA1c) has been recommended for use as a diagnostic tool for diabetes mellitus (DM), but has not been adequately validated in the African population. We aimed to compare HbA1c and the OGTT in the diagnosis of type 2 DM, and to establish the optimal diagnostic cut-off value of HbA1c for diabetes Mellitus among Nigerians. Methods: a cross-sectional population-based screening of 1200 apparently healthy adults was performed using the WHO STEP wise method in Kano, Northwestern Nigeria using a multistage cluster random sampling technique. The fasting plasma glucose (FPG) was performed on subjects who observed the standard protocol (8 12 hour overnight fast) while casual plasma glucose (CPG) estimation was performed on the remaining subjects. HbA1c assay and oral glucose tolerance test (OGTT) were also performed on all subjects who had FPG between 6.1 6.9mmol/l or CPG between 7.8 11.0 mmol/l. The validity of the HbA1c was calculated while the receiver operator characteristics curve was used to establish the optimum diagnostic cut-off value for the HbA1c. Results: HbA1c 5.7- 6.4% identified 2.28% subjects as pre-diabetes. In subjects at high risk of diabetes, the OGTT identified newly diagnosed diabetes in 14 (1.37%) subjects, while the HbA1c 10 (0.98%) subjects. HbA1c cut-off value of ≥ 6.5% compared with FPG had a specificity, sensitivity, positive predictive value and negative predictive value of 63.63%, 98.92%, 70.00% and 98.57% while compared to OGTT, the HbA1c had a specificity, sensitivity, positive predictive value and negative predictive value of 57.14%, 96.49%, 80.00% and 90.16%. Conclusion: the use of glycated haemoglobin as a potential screening and diagnostic approach for T2DM in Nigerian adults at high risk of DM may be useful for its convenience after adjusting for confounders. An HbA1c cut-off value of 6.2% has an optimal sensitivity and specificity of 76.2% and 80.9% and can be used as a screening test.