Relationship between HbA1C and 2-hour post glucose load as a Screening Tool for Type 2 Diabetes Mellitus

Abstract

Objective- To evaluate the performance of HbA1c as a screening tool for type 2 diabetes among Nigerians with systemic hypertension.

Design- Cross-sectional.

Setting- Hospital based study.

Subjects-Two-hundred and seven subjects were recruited, out of which 131had oral glucose tolerance test done. 2-hour post glucose load plasma glucose assay was used as gold standard for the diagnosis of diabetes, thirty three of the subjects also had HbA1c assayed.

Outcome measures- We calculated specificity, sensitivity, positive predictive value, negative predictive value, efficiency of the test and prevalence of the disease using HbA1c. Receiver Operative Characteristic Curve was also plotted and area under the curve determined.

Results- The mean age of the subjects that had HbA1c assay was 53.97±6.27years, while those who did not have HbA1c test had a mean age of 52.85±9.32 which is not significant (p=0.53). The subjects that had the screening test were made up of 24(77.4%) females and 7(22.6%) males. Mean HbA_1C was 6.61±1.93% and mean 2hour plasma glucose was 169.48±93.97mg/dl. The sensitivity of the test was 62.50% (CI=24.49-91.48%), specificity was 65.22% (CI=42.73-83.62%), positive predictive value was 38.46%(CI=13.86-68.42%), negative predictive value was  83.33% (CI=58.58-96.42%), positive likelihood ratio was 1.80, negative likelihood ratio was 0.57, efficiency 61.29, prevalence was 25.81(CI=11.86-44.61). The area under ROC was 0.682 which was significant.

Conclusion- There is a good correlation between HbA1c and 2-hour plasma glucose, however, the performance of this screening test is low compared to the results of previous Caucasian studies.

Keywords: Screening, type 2 diabetes, HbA1c, 2 hour plasma glucose.