The usefulness of glycated hemoglobin A1c (HbA1c) for identifying dysglycemic states in individuals without previously diagnosed diabetes.

Purpose: We investigated HbA1c's validity as a screening parameter for excluding dysglycemic states in the studied population.

Material/methods: Sensitivity and specificity of HbA1c in some cut-off points were compared with diagnoses based on the oral glucose tolerance test (OGTT) in individuals diagnosed between 2009-2010. Receiver operating characteristic (ROC) analysis for HbA1c was conducted. HbA1c and OGGT measures were done in 441 people (253 women, 187 men, average age 40.1 years (18-79 years)). Based on the OGGT test 37 individuals were diagnosed as diabetic, 28 as impaired glucose tolerant (IGT) and 63 as having impaired fasting glycemia (IFG).

Results: A cut-off value of 6.5% HbA1c classifies diabetic subjects with a sensitivity of 45.9% and specificity of 97.5%. In the investigated population the best cut-off point (the highest sum of the sensitivity and specificity) was 5.9% HbA1c (sensitivity 86.6%, specificity 73%). HbA1c values excluding the risk of dysglycemic states have shown false negative rate in 31.9% when HbA1c was 5.5% and 10.6% when HbA1c was 5.0%.

Conclusions: Our results indicate that in the investigated population the evaluation of the prevalence of type 2 diabetes using HbA1c values proposed by the American Diabetes Association (ADA) has unsatisfactory sensitivity and detects less than a half of cases of diabetes based on the OGTT diagnoses. HbA1c 5.7% does not have sufficient specificity to identify individuals not being at risk of any disorder of glucose metabolism.