Long-term cumulative exposure and change patterns of CTI-FI predict the risk of cardiometabolic multimorbidity in middle-aged and older Chinese adults

Background Cardiometabolic multimorbidity (CMM) represents an increasing public health concern among aging populations. We aimed to construct and evaluate a multidimensional index integrating inflammation, metabolism, and physiological function–the CTI-FI (C-reactive protein–triglyceride-glucose and frailty index), and examine its association with incident CMM among middle-aged and older Chinese adults. Methods Data were obtained from the China Health and Retirement Longitudinal Study (CHARLS), a nationally representative prospective cohort. Baseline CTI-FI and cumulative CTI-FI exposure (cuCTI-FI) were calculated, and CTI-FI change patterns were identified using K-means clustering based on repeated measurements. Cox proportional hazards models and restricted cubic spline analyses were performed to evaluate the associations between CTI-FI measures and incident CMM. The incremental value of cuCTI-FI beyond the China-PAR model was assessed using discrimination, calibration-related metrics, and decision curve analysis. Results Among 4,438 participants, higher baseline CTI-FI and cuCTI-FI levels were consistently associated with increased risk of incident CMM in a dose–response manner (both P_trend < 0.001). In fully adjusted models, participants in the highest tertiles of baseline CTI-FI and cuCTI-FI had higher risks of incident CMM (HR: 3.47, 95% CI: 2.62–4.59; and HR: 5.27, 95% CI: 3.92–7.09, respectively). CTI-FI change pattern analysis suggested that participants with persistently higher or increasing CTI-FI levels had greater CMM risk compared with those with stable-low levels (HR: 4.89, 95% CI: 3.78–6.32). Incorporating cuCTI-FI into the China-PAR model improved model discrimination, with AUC increasing from 0.704 to 0.759. The associations remained generally consistent across most subgroup analyses. Conclusions Higher baseline and cumulative CTI-FI levels were associated with increased risk of incident CMM among middle-aged and older Chinese adults. The addition of cuCTI-FI to conventional risk factors provided additional information for CMM risk assessment. Further validation in independent populations is needed to determine its potential application in broader risk assessment settings. Clinical trial number. Not applicable.