Serum Creatinine to Cystatin C as a Marker for Assessing Sarcopenia in Chronic Obstructive Pulmonary Disease – A Single-Center, Prospective, Observational Study

Background: Patients with chronic obstructive pulmonary disease (COPD) can develop systemic complications that include skeletal muscle dysfunction among others. Reduction in muscle mass and function is called as sarcopenia. Diagnosing sarcopenia requires the measurement of walking speed, handgrip strength (HGS), and muscular mass. This is cumbersome to both the patient and the examiner. It requires the use of instruments such as the bio-impedance assay (BIA) and hand dynamometer. Serum cystatin-C (Cys C) and creatinine (Cr) are employed as determinants for kidney function. Cr levels decrease in accordance with low muscle mass, while Cys C remains unchanged. It is due to this relationship among creatinine, cystatin C and muscle mass, serum Cr/Cys C is being tested as a determinant for sarcopenia. Objective: The objective of this study is to study the correlation between Cr-to-Cys C ratio and markers for sarcopenia – appendicular skeletal muscle index (ASMI), handgrip strength, gait speed (GS), and severity of COPD. Materials and Methods: This prospective, observational study was carried out at a tertiary care teaching hospital in Southern India and included patients admitted to the departments of medicine and pulmonology. Patients diagnosed to have COPD were classified according to the GOLD guidelines. Serum Cr and Cys C were measured. Sarcopenia was assessed using BIA for the calculation of ASMI, hand dynamometer for HGS, and 6-m walk test for GS. Results: The results from our study are as follows. The mean for Cr/Cys C was 0.71. Cr/Cys C correlated significantly to ASMI, HGS, GS, and severity of COPD. Conclusion: Serum Cr-to-Cys C ratio can be effectively used for the measurement of sarcopenia in individuals with COPD.