Associations between C-reactive protein-triglyceride glucose index and asthma risk among Chinese adults: evidence from the CHARLS cohort and external hospital-based validation

Background: Inflammation and insulin resistance are important contributors to asthma pathogenesis. However, the association between the C-reactive protein-triglyceride glucose index (CTI), reflecting both systemic inflammation and insulin resistance, and asthma risk remains insufficiently characterized. Methods: A total of 10,234 adults aged ≥45 years were included from the China Health and Retirement Longitudinal Study (CHARLS). The association between CTI and incident asthma was assessed using multivariable Cox proportional hazards models and restricted cubic spline (RCS) analyses, with subgroup analyses performed to explore potential effect modification. An independent hospital-based case-control dataset (277 cases and 277 matched controls) was used for external validation using conditional logistic regression and RCS analyses. Additionally, among patients with asthma in the validation dataset, the associations of CTI with eosinophil and neutrophil counts were evaluated using multivariable linear regression models. Results: During a median follow-up of 84 months, 436 incident asthma cases occurred among 10,234 middle-aged and older adults (incidence, 4.26%), with a mean baseline CTI level of 4.76. After adjustment for potential confounders, higher CTI was consistently associated with an increased risk of asthma, with per 1-unit increase corresponding to a 24% higher risk (HR = 1.24, 95% CI: 1.06-1.45). RCS analyses indicated an approximately linear dose-response relationship. Subgroup analyses showed the associations were more pronounced among participants aged 45-49 years, males, unmarried individuals, and never drinkers. Furthermore, analyses in the hospital-based validation population generally supported the main findings. In the validation dataset, among adults with asthma, per 1-unit increase in CTI was associated with an 8.00% increase in eosinophil counts (95% CI: 4.58%-11.53%) and a 16.72% increase in neutrophil counts (95% CI: 8.24%-25.86%). Conclusions: Higher CTI levels were associated with increased asthma risk in adults and elevated eosinophil and neutrophil counts among adults with asthma.