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HbA1c as a diagnostic tool in subjects at high risk for developing type 2 diabetes

Background and aim: Recently proposed use of HbA1c for the diagnosis of type 2 diabetes had been challenged for poor diagnostic accuracy in comparison to the conventional plasma glucose- based diagnostic tests. While it is obvious that different diagnostic criteria may identify different patient populations, the opportunity to detect undiagnosed diabetes and pre-diabetes with a specific measure of glycaemia, unaffected by high biological variability and preanalytical interferences, remains the major assumed benefit for the use of HbA1c as a diagnostic tool. The aim of this study was to evaluate diagnostic accuracy of HbA1c in subjects at high hisk of developing type 2 diabetes. Methods: Blood samples were taken from the subjects with a previous history of hyperglycaemia, reffered to our clinic for diagnosis of type 2 diabetes. After blood sampling for fasting plasma glucose (FPG) and HbA1c, a 75 g oGTT was performed, followed by a second blood sampling for plasma glucose at 2h (2hPG). Glucose was measured by enzymatic (hexokinase, Olympus AU400, Beckman Coulter, USA), and HbA1c by immunoturbidimetric procedure (TinaQuant HbA1c, Cobas Integra Plus, Roche Diagnostics, USA), respectively. WHO criteria were used to classify patients into diagnostic categories of glycaemia with FPG and 2hPG values. WHO- and ADA-recommended HbA1c values ≥6, 5% (48 mmol/mol), and 5.7-6.4% (39- 47 mmol/mol) were used as diagnostic for diabetes and pre-diabetes, respectively. Results: A total of 317 subjects (M/F: 139/178 ; age range 21-85 years) were included in this study. Multiple regression analysis identified FPG, 2hPG, and age as significant determinants of HbA1c values (P<0, 0001 ; P=0, 0015 and P=0, 0020, respectively). Plasma glucose results classified 70 (22, 1%), 146 (46%) and 101 (31, 9%) of the subjects into categories of normoglycaemia, pre-diabetes and diabetes, respectively. Inter-rater agreement analysis showed fair agreement (κ=0, 350) between HbA1c- and glucose-classification systems, which improved to moderate (κ=0, 431) when two diagnostic categories (normoglycaemia and any hyperglycaemia) were used. Conclusion: Our study revealed a moderate agreement between HbA1c- and glucose-based diagnostic criteria in subjects at high risk for developing type 2 diabetes.

Diabetes; diagnosis; HbA1c

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