The creatinine-to-cystatin C ratio (a surrogate marker of muscle mass) as a predictor of lung function decline in older adults: A nationwide longitudinal study in China

Background Lung function decline is associated with sarcopenia, known as loss of skeletal muscle mass. The serum creatinine to cystatin C ratio (CCR) has been proposed as a biomarker of muscle mass. The associations between CCR and lung function decline are unknown. Methods The study used two waves of data from China Health and Retirement Longitudinal Study (CHARLS) in 2011 and 2015. Serum creatinine and cystatin C were collected at baseline survey (2011). Lung function was assessed by peak expiratory flow (PEF) at 2011 and 2015. Linear regression models adjusted for potential confounders were conducted to analyze the cross-sectional association between CCR and PEF, and the longitudinal association between CCR and annual decline in PEF. Results Totally, 5812 participants aged over 50 years (50.8% women; mean age 63.3 ± 6.5 years) were enrolled in a cross-sectional analysis in 2011, and further 4164 individuals were followed up in 2015. Serum CCR was positively associated with PEF and the PEF% pred. Per 1 SD higher of CCR was associated with 41.55 L/min increases in PEF (p < 0.001) and 10.77 (%) increase in PEF% pred (p < 0.001). Longitudinal analyses indicated that higher CCR level at baseline was related to slower annual decline in PEF and PEF% pred. And this relationship was significant only in women and in never smokers. Conclusions Higher CCR was associated with slower longitudinal PEF decline in women and never smokers. CCR may be a valuable marker to monitor and predict lung function decline in middle-aged and older adults.