Serum-Creatinine-to-Cystatin C-to-Waist-Circumference Ratios as an Indicator of Severe Airflow Limitation in Older Adults

Background: This study aimed to investigate the association between the serum-creatinine-to-cystatin C-to-waist-circumference (CCR/WC) ratio with lung function and severe airflow limitation (SAL). Methods: The data were derived from the China Health and Retirement Longitudinal Study. Peak expiratory flow (PEF) was used as a measure of lung function parameter. Logistic and linear regression were utilized separately to evaluate the relationship between the CCR/WC ratio with PEF and SAL in baseline. Restricted cubic spline was used to explore potential non-linear associations between the CCR/WC ratio and SAL. Cox proportional-hazards models were used to assess the association between CCR/WC quartiles and the risk of new-onset SAL. Results: A total of 6105 participants were included. This study revealed a positive association between the CCR/WC ratio and lung function (PEF: beta [partial coefficient]: 25.95, 95%CI: 12.72 to 39.18, p < 0.001; PEF/PEF (prediction): beta = 0.08, 95%CI: 0.05 to 0.12, p < 0.001) and an inverse association relationship with SAL (OR [odds ratio]: 0.64, 95% confidence interval [CI]: 0.47 to 0.85, p = 0.003). Subgroup analysis showed a significant association between the CCR/WC ratio and SAL in males (OR: 0.58, 95% CI: 0.37 to 0.90, p = 0.017) but not in females (p = 0.059). Cox regression analysis revealed a decreased risk of SAL in the quartiles (Q2-4) compared to the first quartile of the CCR/WC ratio (hazard ratios [HRs]: 0.49 to 0.73, all p < 0.05). Conclusions: This study highlights a positive association between the CCR/WC ratio and lung function, with a potential protective effect against SAL.