The joint effect of triglyceride-glucose index and C-reactive protein levels on the risk of chronic obstructive pulmonary disease: a prospective cohort study.

Background: The triglyceride-glucose index (TyG) and C-reactive protein (CRP) are key biomarkers on clinical diagnosis, each related to lung dysfunction. However, the relationship of both indexes with the risk of chronic obstructive pulmonary disease (COPD) is still unclear. This study purposes to focus on the individual and joint associations of TyG and CRP levels with COPD risk.

Methods: This cohort study utilized baseline TyG and CRP data from the UK Biobank. Hazard ratios (HRs) and 95% confidence intervals (CIs) for COPD risk associated with TyG and CRP levels were calculated through Cox regression models. Receiver operating characteristic (ROC) curves were conducted to determine the optimal cut-off values for TyG and CRP, which were combined into a joint variable. Kaplan-Meier (KM) method was utilized to analyze cumulative hazard, while joint analysis was employed for evaluating the joint risk. Stratified and sensitivity analyses were also performed to assess the associations within subgroups, and mediation effect of TyG on COPD risk via CRP levels was assessed.

Results: This study enrolled 385,523 individuals, with 10,515 COPD cases were recorded in follow-up. Compared to the lowest quintile, individuals with higher TyG and CRP had increased risk of COPD (all HRs > 1.00). The optimal cut-off values of TyG and CRP were 7.14 and 1.88 mg/L, and we found that the simultaneous elevation of both TyG and CRP significantly increased the risk of COPD. Moreover, the joint effect was stronger in participants younger than 60 years old, males, smokers or passive smokers, those with body mass index (BMI) < 25.0 kg/m², and those without baseline diabetes, asthma, or a family history of respiratory diseases (P _{for interaction} < 0.05). Moreover, the effect of TyG on COPD was significantly mediated by CRP, explaining almost 15.6% of this influence.

Conclusions: These results underscored the individual and joint effects of TyG and CRP upon COPD risk, indicating their usefulness as biomarkers for early risk assessment.