Is HbA1c a good screening test for diabetes mellitus?

ObjectivesHbA1c has been recently recommended as the primary diagnostic test for diabetes. This study evaluated the positive predictive value (PPV) and negative predictive value (NPV) of HbA1c against the oral glucose tolerance test (OGTT) in three locations.Design and methodsThree years of data with concurrent OGTT and HbA1c tests were extracted from Laboratory Information Systems (LIS) and receiver operator (ROC) curves and positive and negative predictive values calculated comparing the OGTT with the HbA1c values using a 10% prevalence of diabetes.ResultsThe recommended threshold HbA1c value of 6.5% did not give the optimal combination of NPV (0.93 to 0.92) and PPV (0.40 to 0.61) compared to a threshold HbA1c value of 7.0% (NPV 0.91 to 0.92, PPV 0.61 to 0.73).ConclusionThe optimal HbA1c value for the diagnosis of diabetes is 7.0% but even at this HbA1c the PPV is suboptimal and may cause up to 12% of patients without diabetes, as defined by a normal OGTT, to be classified having diabetes mellitus.

► This paper describes a study comparing 2 tests, the long used OGTT and the recently recommended HbA1c, for screening/diagnosis of diabetes.
► The study is multi institution and uses the NHANES data as a reference point for comparison of results.
► The positive predictive value for the recommended threshold HbA1c value of 6.5% is only 0.4 and the test may not be suitable for screening.