A new index based on serum creatinine and cystatin C is useful for assessing sarcopenia in patients with advanced cancer

Sarcopenia is a well-known risk factor for inferior cancer outcomes, but the identification of patients at risk remains challenging. A new sarcopenia index (SI), defined as serum creatinine (Cr) × cystatin C (CysC)-based glomerular filtration rate (eGFR_CysC), has been reported to be an objective surrogate marker for sarcopenia. The aim of this study was to assess whether the SI is associated with sarcopenia and cancer-related fatigue (CRF) in patients with advanced cancer.

This cross-sectional study included 182 patients with different types of cancer (cancer stages III/IV; mean age 55.1 ± 11.1 y). Sarcopenia was defined as the presence of both low muscle mass and low muscle strength. The cross-sectional area of skeletal muscle mass (SMA) at the third lumbar spine was estimated by computed tomography (CT). Low muscle mass was defined as a skeletal muscle index (SMA/height²) <34.9 cm²/m² for women and 40.8 cm²/m² for men. Low muscle strength was determined by handgrip strength (HGS) according to the cutoffs of the Asian Working Group for Sarcopenia (<18 kg for women and <26 kg for men). CRF was measured by the Brief Fatigue Inventory (BFI). The associations between SI with both sarcopenia and CRF were investigated.

The prevalence of sarcopenia was 27.5%. The SI was significantly lower in both the sarcopenia and severe fatigue groups. The associations between SI and SMA (r = 0.365; P < 0.001), skeletal muscle index (SMI) (r = 0.340; P < 0.001), and HGS (r = 0.414; P <0 .001) were stronger than the associations between the serum creatinine/cystatin C (Cr/CysC) ratio and SMA (r = 0.299; P < 0.001), SMI (r = 0.269; P <0 .001), and HGS (r = 0.364; P <0 .001). Additionally, a decrease in the SI was associated with a higher likelihood of sarcopenia (odds ratio per 10-unit, 1.09; 95% confidence interval, 1.02-1.16) after adjusting for potential confounding factors. However, there was only a weak correlation between the SI and BFI score (r = -0.161, P = 0.045).

The SI might be a useful objective tool for assessing sarcopenia in patients with advanced cancer. Further studies are warranted to extend the present findings.