Value of Cystatin C-Based Sarcopenia Index in Patients Undergoing Surgery for Renal Tumors

Sarcopenia is a condition of low muscle strength and quantity, severe if low physical performances. The sarcopenia index (SI), calculated by blood levels of creatinine and cystatin C, had been reported to be correlated with skeletal muscle mass and is a potential simple screening tool for sarcopenia. We hypothesized that patients with a low SI, meaning low muscle mass, would have an inflated estimated glomerular filtration rate (eGFR) value based on serum creatinine levels. We also tested the prognostic value of the SI in a cohort of patients who had surgery for renal malignancies. We conducted a retrospective, observational study of 322 patients that had surgery for renal tumors in National Cancer Center Hospital East (Kashiwa, Chiba) between April 2017 and June 2023. We assessed sarcopenia measuring psoas muscle index (PMI), psoas muscle density (PMD), and skeletal muscle area (SMA) by computed tomography. We assessed the association between SI and eGFR before and after surgery. We also assessed the association between SI and postoperative outcome, including overall survival. Of the 322 patients, 211 (66%) were males, with a median age of 69 years. SI had a weak correlation with both PMI and PMD in males (PMI: ρ = 0.25; PMD: ρ = 0.21). In females, SI and PMD exhibited a low correlation (ρ = 0.26), while SI and PMI displayed an insignificant correlation (ρ = 0.19). The correlation between SMA and SI was moderate for both males and females (males: ρ = 0.51; females: ρ = 0.46). After radical nephrectomy, eGFR decreased in 98% of patients with high SI, compared to 69% of patients with low SI. We also demonstrated that low SI predicted poor prognosis. Clinicians can recognize the possibility of overestimated eGFR in the low SI group by measuring SI around the surgery. Low SI may also help predict poor prognosis. We assessed the value of sarcopenia Index (SI) in 322 patients who underwent surgery for renal tumors. We found that low SI was associated with poor prognosis and could cause the overestimation of estimated glomerular filtration rate based on serum creatinine. Calculating SI by measuring blood cystatin C might be useful for patients who require surgery for renal tumors.