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Creatinine Versus Cystatin C: Differing Estimates of Renal Function in Hospitalized Veterans Receiving Anticoagulants
Christina Hao Wang1,2, Anna D Rubinsky3, Tracy Minichiello1
1San Francisco Veterans Affairs Medical Center, San Francisco, CA, USA.
Insights
Serum creatinine may be unreliable for estimating kidney function in patients on anticoagulation. Cystatin C offers a more accurate eGFR, potentially altering drug dosing for 31-52% of patients.
Area of Science:
- Nephrology
- Pharmacology
- Internal Medicine
Background:
- Current anticoagulation dosing relies on kidney function estimated by serum creatinine.
- Serum creatinine can be unreliable due to variations in muscle mass.
- Cystatin C provides an alternative, muscle-independent estimation of glomerular filtration rate (eGFR).
Purpose of the Study:
- Compare cystatin C-based eGFR (eGFRcys) with creatinine-based eGFRs in hospitalized patients on anticoagulation.
- Assess discordant results that could impact medication dosing.
- Evaluate the reclassification of patients into drug-dosing categories based on eGFR estimates.
Main Methods:
- Retrospective chart review of 75 hospitalized veterans receiving non-vitamin K antagonist anticoagulation.
- Collected same-day measurements of cystatin C and creatinine.
- Compared eGFRcys with three creatinine-based equations (CKD-EPI, MDRD, Cockcroft-Gault) and analyzed patient reclassification.
Main Results:
- Cystatin C predicted lower eGFR compared to creatinine-based equations (median differences: -7.1 to -25.9 mL/min/1.73 m2).
- 31-52% of patients were reclassified into lower drug-dosing categories using cystatin C.
- Substantial discordance was observed between cystatin C and creatinine eGFR estimates.
Conclusions:
- Significant discordance exists between cystatin C and creatinine eGFR in anticoagulated inpatients.
- Findings suggest potential impact on medication dosing.
- Further research is needed to confirm findings and evaluate clinical outcomes.
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 (eGFRcys) 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 (eGFRcys) and eGFRs using three creatinine-based equations: CKD-EPI (eGFREPI), Modified Diet in Renal Disease (eGFRMDRD), and Cockcroft-Gault (eGFRCG). 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 eGFREPI, - 21.2 (IQR - 43.7, - 8.1) mL/min/1.73 m2 versus eGFRMDRD, and - 25.9 (IQR - 46.8, - 8.7) mL/min/1.73 m2 versus eGFRCG. 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.
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