IGFBP4 and obstructive sleep apnea syndrome: The BMI-stratified analysis (Supplementary Table 1) revealed significant differences in ESS, OSA indices (AI, HI, AHI), HbA1c, C-peptide, insulin, IGFBP4, and leptin levels in the obese group, consistent with obesity being an independent contributor to OSA severity and metabolic dysregulation.