Ratio That Reveals Risk: Defining TG:HDL-C Ratio Cutoff for Insulin Resistance in Adolescents with Obesity

Background/Objectives: Insulin resistance (IR) plays a central role in metabolic dysfunction and elevates the risk of chronic diseases such as type 2 diabetes mellitus in later life. Early identification of IR in adolescents is therefore important. This study aimed to determine the triglyceride-to-high-density lipoprotein cholesterol (TG:HDL-C) ratio cutoff for IR and assess its association with IR predictors among adolescents with obesity. Methods: A total of 215 blood samples from adolescents aged 13–16 years with obesity were analyzed for fasting blood glucose, lipids, insulin, leptin, and adiponectin. Obesity was defined using BMI z-scores, while IR was classified using the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR ≥ 4.0). Receiver operating characteristic (ROC) analysis was performed to compare the discriminatory performance between the TG:HDL-C ratio and Leptin:Adiponectin ratio (LAR). Multiple logistic regression was performed to assess associations between the TG:HDL-C ratio and IR-related markers. Results: The area under the ROC curve for the TG:HDL-C ratio was comparable to LAR (0.73 vs. 0.68, p = 0.3). The optimal TG:HDL-C ratio cutoff identified using the maximum Youden index was 0.89, with 62% sensitivity and 75% specificity. A TG:HDL-C ratio ≥ 0.89 was associated with higher odds of elevated insulin (AOR 1.1, 95% CI 1.0–1.13), elevated HbA1c (AOR 2.7, 95% CI 1.1–6.6), abdominal obesity (AOR 3.6, 95% CI 1.9–6.7), and raised LAR (AOR 1.2, 95% CI 1.0–1.5). Conclusions: These findings suggest that a TG:HDL-C ratio cutoff of 0.89 may be a useful marker for identifying IR in adolescents with obesity.