Discrepancies Between Creatinine- and Cystatin C-Based eGFR Estimation in Palliative Care Patients and Their Implications on Drug Dosing.

Background: Palliative care patients often experience sarcopenia, which can cause overestimation of kidney function by creatinine-based estimated glomerular filtration rate (eGFR) and inappropriate drug dosing. Data on cystatin C (CysC) use are scarce. Objectives: To examine intra-individual differences between creatinine- and CysC–based eGFR in palliative patients and assess the frequency of renally eliminated drugs prescribed. Design: Retrospective, single-center cohort study. Setting/Subjects: All patients admitted in 2023 to the palliative care unit of the University Hospital Zurich, Switzerland. Of 206 patients, 178 had eGFR data, and 144 with consent were included. Measurements: Data including creatinine, CysC, and prescribed medications were extracted from electronic records. eGFR was calculated using Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2009 (creatinine) and CKD-EPI 2012 (CysC, combined). Intraindividual discrepancies >15 mL/min/1.73m 2 were defined as clinically relevant. Results: Paired values were available for 85 patients; 53% showed clinically relevant discrepancies (median 17 mL/min/1.73m 2 ). In 22% of patients the discrepancy exceeded 30 mL/min/1.73m 2 . Diabetes was the only factor associated with differences. Acute kidney injury (AKI) occurred in 32% and was strongly linked to mortality, whereas discrepancies were not. Patients received a median of 19 drugs; of the 20 most frequently prescribed, 7 were renally eliminated. Over one-third with relevant discrepancies received two such drugs. Conclusions: Clinically relevant eGFR discrepancies are common in palliative care patients and may cause misclassification and dosing errors. CysC testing should be used selectively when prescribing renally eliminated drugs with toxicity risk, underscoring the need for individualized prescribing and prospective validation.