BACKGROUND: To investigate whether composite lipid indices and remnant cholesterol (RC) are associated with electrophysiological severity in carpal tunnel syndrome (CTS) and to evaluate their independent discriminative performance for advanced disease stage. METHODS: In this cross-sectional case-control study, 124 patients with electrophysiologically confirmed CTS and 113 age- and sex-matched controls were included. CTS severity was graded according to the Padua classification. Fasting lipid profiles were obtained, and composite atherogenic indices including the triglyceride-to-high-density lipoprotein ratio (TG/HDL), the non-HDL/HDL ratio, and the atherogenic index of plasma (AIP) and RC were calculated. Between-group and severity-based comparisons were performed. Multivariable logistic regression was used to assess independent associations with advanced CTS (moderate-severe vs. mild), and receiver operating characteristic (ROC) analyses evaluated discriminative performance. RESULTS: CTS patients exhibited higher glucose, HbA1c, LDL-cholesterol, total cholesterol, and RC levels than controls (all p < 0.05), whereas composite indices did not significantly differ between groups. Within the CTS cohort, lipid parameters, composite indices, and RC varied significantly across electrophysiological stages. In multivariable analysis adjusted for age and sex, non-HDL/HDL ratio (OR = 2.99, 95% CI: 1.44-6.23), RC (OR = 3.12, 95% CI: 1.03-9.45), and AIP (OR = 0.27, 95% CI: 0.10-0.77) remained independently associated with advanced stage. The final model demonstrated moderate discriminative performance (area under the receiver operating characteristic curve [AUC] = 0.715, 95% CI: 0.619-0.811). CONCLUSION: Composite lipid indices and RC are independently associated with electrophysiological severity rather than CTS presence. These findings support a severity-oriented metabolic framework in which systemic atherogenic burden may amplify median nerve dysfunction.