RESUMEN
AIMS: The results of using HbA1C-based criteria for diagnosis of type 2 diabetes and prediabetes have been reported to differ from those obtained using fasting plasma glucose (FPG) or an oral glucose tolerance test (OGTT). We aimed to determine whether these discrepancies might be due to the influence of the glycation gap. METHODS: For 430 patients without previously diagnosed diabetes for whom an OGTT had been requested in normal clinical practice, FPG, fructosamine and HbA1C were measured at the time of the test and again 1 month later. Glycaemia/diabetes status was classified as normoglycaemia, prediabetes or diabetes using both HbA1C-based and FPG/OGTT-based criteria, and their glycation gaps GG were calculated. RESULTS: The specificity of an HbA1C level of 6.5 % (48 mmol/mol) for diagnosis of FPG/OGTT-defined type 2 diabetes was 99 %, but its sensitivity was less than 37 %. HbA1C-diabetic patients had higher average blood glucose levels than FPG/OGTT-diabetic patients. With either set of criteria, high-GG patients were disproportionately numerous among those classified as diabetic and were disproportionately infrequent among those classified as normoglycaemic, but the effect was greater for the HbA1C criteria. CONCLUSIONS: The differences between HbA1C-based and FPG/OGTT-based diagnoses are largely due to the influence of the glycation gap, which may also influence the early stages of FPG/OGTT-defined diabetes.