Endocrine Abstracts

Introduction: Recently, the American Diabetes Association has proposed glycated hemoglobin (HbA1c) as a diagnostic criteria for diabetes (HbA1c≥6.5%) and prediabetes (5.7%≤HbA1c≤6.4%).

Aims: To compare HbA1c with fasting glucose and oral glucose tolerance test (OGTT) as diagnostic criteria for diabetes and prediabetes, in obese patients; to calculate its sensitivity and specificity when compared with standard diagnostic criteria.

Materials and methods: We studied 417 obese patients (73 men) without previous diagnosis of diabetes or prediabetes with mean age=41.8±12.4 years, BMI=46.6±7.2 kg/m² and waist circumference=124.7±16.1 cm. They were submitted to a fasting blood collection for glucose and HbA1c assessments, followed by a classic 75 g OGTT. Patients were divided in diagnostic groups (normal values, prediabetes and diabetes) according to HbA1c or OGTT, and we studied the concordance degree between groups.

Results: The mean fasting glucose=95.2±19.6 mg/dl, 2nd hour glucose=127.8±54 mg/dl and HbA1c=5.73±0.78%. According OGTT criteria, 232 patients (55.6%) showed normoglycemia, 135 (32.4%) prediabetes (impaired fasting glucose IFG=49; impaired glucose tolerance IGT=53; IFG+IGT=33) and 50 (12%) diabetes. Based on HbA1c criteria, 221 patients (53%) had normal HbA1c, 151 (36.2%) prediabetes and 45 (10.8%) diabetes. Comparing both criteria classifications, there was a significant difference (P<0.001) between diagnostic groups. HbA1c as diagnostic criteria for diabetes and prediabetes showed, respectively, a sensitivity of 50 and 45.2% and a specificity of 55.6 and 40.4%. Comparing both diagnostic methods, no significant difference for gender was found.

Conclusion: Diabetes and prediabetes are highly prevalent in the obese population, by either HbA1c or glucose criteria. However, each method identifies different groups of patients with abnormal control of carbohydrate metabolism. Comparing with the standard criteria for diabetes and prediabetes (based on glucose values), HbA1c shows low sensitivity and specificity as diagnostic criteria for carbohydrate dysmetabolism in the obese population.