Association of creatinine-to-cystatin C ratio with computed tomography measures of skeletal muscle quantity and quality: The multi-ethnic study of atherosclerosis.

Background & Aims: Skeletal muscle (SM) health has significant prognostic value in geriatric and chronic disease populations, yet its assessment is frequently omitted due to challenges in evaluation. The creatinine-to-cystatin C ratio (CCR) is a simple serum-based measure that associates well with measured SM quantity (myopenia) and strength, but evidence for its association with SM quality (myosteatosis) is limited and conflicting. This study investigated the association between CCR and computed tomography (CT) measures of myopenia and myosteatosis.

Methods: In this cross-sectional analysis of the Multi-Ethnic Study of Atherosclerosis, 1035 participants with complete body composition measurements and visit-matched serum creatinine and cystatin C measurements were included. CCR was calculated as (serum creatinine/serum cystatin C) x 100. Myopenia was quantified as SM index (SMI; SM area normalized for body surface area) and myosteatosis as SM density (SMD; based on Hounsfield units) from CT images. Correlation analyses and multivariable linear regression were used to model the relationships of CCR with SMI and SMD.

Results: CCR was positively correlated and associated with SMI (rho = 0.295, p < 0.001; adjusted β 0.071 per 1 % increase in CCR, standard error [SE] 0.032, 95 % confidence interval [CI] 0.009 to 0.133, p = 0.026) and SMD (rho = 0.417, p < 0.001; adjusted β 0.040 per 1 % increase in CCR, SE 0.006, 95 % CI 0.027 to 0.052, p < 0.001). However, the associations were weaker in participants with chronic kidney disease (CKD), particularly for SMD (interaction p = 0.005).

Conclusions: CCR is associated with CT measures of myopenia and myosteatosis; however, it should be used cautiously in patients with CKD.