Insulin resistance surrogate indices and papillary thyroid carcinoma in patients with thyroid nodules undergoing surgery

Background Metabolic abnormalities may be associated with thyroid cancer-related metabolic profiles, whereas body mass index (BMI)-based assessment may not fully capture metabolic heterogeneity. This study investigated the associations between insulin resistance surrogate indices reflecting glucose and lipid metabolic alterations and papillary thyroid carcinoma (PTC) among patients with thyroid nodules undergoing surgery. Methods This retrospective case-control study included 4,047 patients with thyroid nodules (3,415 PTC and 632 benign thyroid nodules). Three insulin resistance surrogate indices, including the triglyceride-glucose (TyG) index, metabolic score for insulin resistance (METS-IR), and triglyceride-to-high-density lipoprotein cholesterol ratio (TG/HDL-C), were calculated from routinely available clinical parameters. Multivariable logistic regression and restricted cubic spline analyses were performed, with additional BMI-stratified analyses and interaction testing. Results Patients with PTC had higher levels of TyG, METS-IR, and TG/HDL-C than those with benign nodules. After adjustment for age, sex, BMI, diabetes mellitus, lipid-lowering therapy, smoking status, and alcohol consumption, TyG (OR 1.42, 95% CI 1.20–1.68, P < 0.001) and METS-IR (OR 1.05, 95% CI 1.02–1.08, P < 0.001) remained associated with higher odds of PTC, whereas TG/HDL-C was not statistically significant (OR 1.07, 95% CI 0.99–1.16, P = 0.081). Restricted cubic spline analyses showed significant overall associations of TyG and METS-IR with PTC, with evidence of nonlinear relationships. BMI-stratified analyses showed associations between TyG and METS-IR and PTC in participants with BMI ≤28 kg/m 2 , whereas similar associations were not statistically significant in participants with BMI >28 kg/m 2 . However, interaction tests did not provide statistical evidence that BMI modified these associations. Conclusions Higher levels of TyG and METS-IR were associated with higher odds of PTC after multivariable adjustment. These findings suggest that TyG and METS-IR may provide additional information for characterizing metabolic profiles among patients undergoing surgery for thyroid nodules.