Obesity alters glucose metabolism, raising challenges in interpreting glycemic diagnostic tests. 

A study published in Journal of Diabetes Research compared the performance of glycated hemoglobin (HbA1c) and oral glucose tolerance test (OGTT) across body mass index (BMI) categories, with a focus on morbid obesity. 

The analysis included 1031 patients (86.8% female) who underwent metabolic assessment. Based on BMI, patients were grouped as nonobese, obese, or morbidly obese. 

Dysglycemia prevalence was 43.1% when defined by HbA1c and 30.9% by OGTT. In morbidly obese patients, HbA1c identified more cases of dysglycemia (p < 0.001), whereas OGTT did not show intergroup difference (p = 0.117). 

Agreement between HbA1c and OGTT was low (κ = 0.326). 

Further analysis showed that HbA1c, insulin, HOMA-IR, CRP, and triglycerides increased progressively with BMI. Elevated insulin was linked with HbA1c-defined dysglycemia, indicating hyperinsulinemia may blunt OGTT response.

The findings indicate HbA1c may be more effective in identifying early metabolic disturbances in obese and morbidly obese patients compared to OGTT. in morbid obesity. The study emphasizes the importance of considering BMI and insulin status when selecting and interpreting glycemic diagnostic tests.