Challenges in renally eliminated medication use: Evaluating cystatin C and serum creatinine eGFR discordance.

Background: Accurately estimating glomerular filtration rate (GFR) is crucial for dosing medications in hospitalized patients. Due to limitations of serum creatinine for GFR estimation, serum cystatin C (CysC) has been explored as an alternative functional kidney biomarker. This study assessed discordance between eGFR_Cr and eGFR_CysC in a large sample of hospitalized patients and examined the frequency of renally eliminated medications affected by eGFR discordance.

Methods: This multisite historical study included adults hospitalized between 2011 and 2023 with CysC and serum creatinine reported within 24 h of each other. The first concurrent biomarker pair for each patient was analyzed. eGFR discordance and use of renally eliminated medications were described.

Results: 17,718 hospitalized patients with concurrent creatinine and CysC assessments were included. The median eGFR_Cr was 65 mL/min, and the eGFR_CysC was 46 mL/min. The median absolute difference of eGFR_Cr-eGFR_CysC was 15 mL/min, and 7972 patients (45%) had a > 30% absolute difference. There was a significantly greater percentage of patients with an eGFR <30 mL/min based on eGFR_CysC (26%) compared to eGFR_Cr (15%) (p < 0.001). Patients were prescribed an average of 20 medications in the 24 h surrounding the concurrent biomarker assessment. Renally eliminated medications accounted for 39% ± 13% of medication orders, and 80% of patients with eGFR discordance were prescribed five or more renally eliminated medications.

Conclusion: Substantial eGFR discordance between eGFR_CysC and eGFR_Cr was observed in hospitalized patients, which directly affects the dosing of renally eliminated medications. Further research is needed to optimize the pharmacotherapy of renally eliminated medications with discordant GFR assessments to improve medication safety and effectiveness.