Comparison of International Expert Committee value of HbA1c and WHO criteria for the diagnosis of Type 2 diabetes

Abstract

Background: The international expert committee recommendations on the use of HbA1c in the diagnosis of diabetes mellitus has just come on board. Thus, it is imperative to compare its performance with existing accepted standard for diagnosing diabetes mellitus.
Objective: To use the new cut-off value of HbA1c of >6.5% as a diagnostic tool for type 2 DM among African blacks with systemic hypertension.
Methodology: Two-hundred and seven subjects attending the out-patient department of Lagos University Teaching Hospital were recruited, out of which 131 of the subjects had oral glucose tolerance test done. Plasma glucose value of >200mg/dl at 2-hours was used as standard for diagnosis of diabetes. Thirty one of the subjects had HbA1c done. HbA1c of >6.5% was considered to be positive for diabetes. A 2x2 table was made to calculate specificity, sensitivity, positive predictive value, negative predictive value, efficiency of the test. The Prevalence of diabetes by HbA1c and WHO criteria were calculated.
Results: The mean age of the subjects that had HbA1c assay was 54.3±6.6years. The subjects were made up of 25(80.6%) females and 6(19.4%) males. Mean HbA1C was 6.6% and mean 2hour plasma glucose was 169.47mg/dl. HbA1c had a sensitivity of 73.91%%, specificity of 62.5%, positive predictive value of 85%%, negative predictive value of 41.66%, efficiency of 70.97%. Prevalence of diabetes mellitus by HbA1c and WHO criteria were 35.1% and 25.8% respectively. The correlation between HbA1c and 2hour plasma glucose was 0.73, r square 0.53 (P v = 0.000).
Conclusion: The current cut off value of HbA1c for diagnosis of diabetes mellitus has performed better than the cut off of >6.1%.

Keywords: Diabetes mellitus –HbA1c-oral glucose tolerance test