HbA(1c) measurement for the diagnosis of diabetes: is it enough?

To analyse the performance of HbA(1c) in diagnosing Type 2 diabetes based on fasting plasma glucose and/or 2-h plasma glucose measurements after a 75-g oral glucose tolerance test.

This is a study of diagnostic test accuracy in individuals referred to the Clinical Pathology Department for oral glucose tolerance testing. After fasting overnight, HbA(1c), fasting plasma glucose and 2-h plasma glucose were measured. The receiver operating characteristic curve was used to evaluate the diagnostic performance of HbA(1c).

Four hundred and ninety-eight subjects (195 male, mean age 56 years) were enrolled and 115 (23.1%) were diagnosed with diabetes according to glucose-based methods and only 56 (11.2%) individuals were identified by HbA(1c) ≥ 6.5% (48 mmol/mol) (sensitivity 20.9%, specificity 95.3%). There is poor agreement between the newly recommended criterion and the current glucose-based diagnostic criteria (κ = 0.217; P < 0.001), probably because the diagnostic methods identify different populations of patients. Adding a glucose-based method into an algorithm, as proposed by the UK Department of Health, improved HbA(1c) performance.

HbA(1c) ≥ 6.5% (48 mmol/mol) showed limited sensitivity to diabetes diagnosis, although with high specificity. The results suggest that this cut-off point would not be enough to diagnose diabetes. Its use as the sole diabetes diagnostic test should be interpreted with caution to assure the correct classification of diabetic individuals.