Comparative study of HbA1c and fasting plasma glucose vs the oral glucose tolerance test for diagnosis of diabetes in people with tuberculosis

AimTo compare HbA(1c) and fasting plasma glucose assessment, with the 2-h oral glucose tolerance test as reference, in screening for diabetes in people with turberculosis. MethodsIndividuals (N=268) with newly diagnosed smear-positive tuberculosis were screened for diabetes at a tertiary hospital in Lahore, Pakistan. Diabetes diagnosis was based on WHO criteria: thresholds were 48 mmol/mol (6.5%) for HbA(1c) and 7.0mmol/l for fasting plasma glucose. ResultsThe proportion of participants diagnosed with diabetes was 4.9% (n =13) by oral glucose tolerance test, while 11.9% (n =32) and 14.6% (n =39) were diagnosed with diabetes using HbA(1c) and fasting plasma glucose criteria, respectively. The area under the receiver-operating characteristic curve was 0.79 (95% CI 0.64 to 0.94) for HbA(1c) and 0.61 (95% CI 0.50 to 0.73) for fasting plasma glucose, with a borderline significant difference between the two tests (P=0.07). ConclusionsHbA(1c) and fasting plasma glucose performed equally in terms of diagnosing new diabetes cases in individuals with tuberculosis, but the proportion of participants falsely classified as positive was higher for fasting plasma glucose. This may be explained by acute blood glucose fluctuations when using fasting plasma glucose. HbA(1c) may be a more reliable test in individuals with transient hyperglycaemia.