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.

Automated summary

Background: There is a correlation between decline in lung function and sarcopenia, characterized by loss of skeletal muscle mass. The serum creatinine to cystatin C ratio (CCR) has been suggested as a biomarker for muscle mass. However, the relationship between CCR and lung function decline is not yet known. Methods: Data from the China Health and Retirement Longitudinal Study (CHARLS) in 2011 and 2015 was used. Serum creatinine and cystatin C were measured in 2011, and lung function was assessed by peak expiratory flow (PEF) in both 2011 and 2015. Linear regression models were used to analyze the association between CCR and PEF, adjusting for potential confounders. Results: The study included 5812 participants over the age of 50 (50.8% women; mean age 63.3 +/- 6.5 years) in a cross-sectional analysis in 2011, with 4164 individuals followed up in 2015. Serum CCR was found to be positively associated with PEF and PEF% pred. Every 1 standard deviation increase in CCR was associated with a 41.55 L/min increase in PEF (p < 0.001) and a 10.77% increase in PEF% pred (p < 0.001). Longitudinal analysis showed that higher CCR at baseline was associated with a slower annual decline in PEF and PEF% pred. This relationship was significant only in women and never smokers. Conclusions: A higher CCR is associated with a slower decline in lung function in women and never smokers. CCR may be a valuable marker for monitoring and predicting lung function decline in middle-aged and older adults.