High-sensitivity C-reactive protein–triglyceride-glucose composite index and reduced estimated glomerular filtration rate in adults undergoing routine health examinations: a cross-sectional study

Background Reduced kidney function often develops in parallel with metabolic dysregulation and chronic low-grade inflammation, yet practical markers that capture both processes remain limited in routine screening settings. We evaluated whether the high-sensitivity C-reactive protein–triglyceride-glucose composite index (CTI), an integrated marker derived from hs-CRP and the triglyceride-glucose index, was associated with reduced estimated glomerular filtration rate (eGFR) in adults undergoing health examinations. Methods This cross-sectional study included 1429 adults with complete core variables from an independent hospital-based cohort established at the Health Examination Center of the Second Affiliated Hospital of Shandong First Medical University between June 2024 and December 2025. CTI was calculated as TyG + 0.412 × ln [hs-CRP (mg/L)], where TyG = ln [TG (mg/dL) × fasting plasma glucose (mg/dL)/2]. The primary outcome was single-occasion reduced eGFR, defined as <90 mL/min/1.73 m², and was not interpreted as chronic kidney disease. Multivariable logistic regression, restricted cubic spline analysis, receiver operating characteristic analysis, subgroup analysis, variance inflation factor diagnostics, and sensitivity analyses were performed. Results The mean (SD) age was 48.8 (11.3) years, 46.8% of participants were women, and 398 individuals (27.9%) had single-occasion reduced eGFR. The prevalence of reduced eGFR increased across CTI quartiles, from 12.8% in the lowest quartile to 45.7% in the highest quartile. After adjustment for demographic factors, lifestyle factors, cardiometabolic comorbidities, and uric acid, each 1-SD increment in CTI was associated with 45% higher odds of reduced eGFR (odds ratio [OR], 1.45; 95% CI, 1.11-1.90). Compared with the lowest quartile, the highest quartile showed an OR of 2.11 (95% CI, 1.07-4.17), whereas the adjusted linear trend across quartiles was borderline (P for trend = .056). Only 1 participant (0.1%) had eGFR <60 mL/min/1.73 m²; using a stricter eGFR <75 mL/min/1.73 m² threshold yielded a directionally similar but borderline association (OR, 1.75; 95% CI, 0.99-3.10). CTI discriminated reduced eGFR modestly but better than TyG, hs-CRP, and remnant cholesterol. Conclusions In this health examination population, higher CTI was independently associated with a higher prevalence of single-occasion reduced eGFR. Because discrimination was modest and the design was cross-sectional, CTI should be interpreted as an adjunctive marker of metabolic-inflammatory burden rather than a diagnostic or predictive tool. Prospective validation is required.