Creatinine Versus Cystatin C: Differing Estimates of Renal Function in Hospitalized Veterans Receiving Anticoagulants

Abstract

Background: Current practice in anticoagulation dosing relies on kidney function estimated by serum creatinine using the Cockcroft-Gault equation. However, creatinine can be unreliable in patients with low or high muscle mass. Cystatin C provides an alternative estimation of glomerular filtration rate (eGFR) that is independent of muscle.

Objective: We compared cystatin C-based eGFR (eGFR_cys) with multiple creatinine-based estimates of kidney function in hospitalized patients receiving anticoagulants, to assess for discordant results that could impact medication dosing.

Design: Retrospective chart review of hospitalized patients over 1 year who received non-vitamin K antagonist anticoagulation, and who had same-day measurements of cystatin C and creatinine.

Participants: Seventy-five inpatient veterans (median age 68) at the San Francisco VA Medical Center (SFVAMC).

Main measures: We compared the median difference between eGFR by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) study equation using cystatin C (eGFR_cys) and eGFRs using three creatinine-based equations: CKD-EPI (eGFR_EPI), Modified Diet in Renal Disease (eGFR_MDRD), and Cockcroft-Gault (eGFR_CG). We categorized patients into standard KDIGO kidney stages and into drug-dosing categories based on each creatinine equation and calculated proportions of patients reclassified across these categories based on cystatin C.

Key results: Cystatin C predicted overall lower eGFR compared to creatinine-based equations, with a median difference of - 7.1 (IQR - 17.2, 2.6) mL/min/1.73 m² versus eGFR_EPI, - 21.2 (IQR - 43.7, - 8.1) mL/min/1.73 m² versus eGFR_MDRD, and - 25.9 (IQR - 46.8, - 8.7) mL/min/1.73 m² versus eGFR_CG. Thirty-one to 52% of patients were reclassified into lower drug-dosing categories using cystatin C compared to creatinine-based estimates.

Conclusions: We found substantial discordance in eGFR comparing cystatin C with creatinine in this group of anticoagulated inpatients. Our sample size was limited and included few women. Further investigation is needed to confirm these findings and evaluate implications for bleeding and other clinical outcomes.

Nih trial registry number: Not applicable.

Keywords: anticoagulation; atrial fibrillation; chronic kidney disease (CKD); cystatin C; venous thromboembolism.