Prospective Comparison of Urinary Measured Creatinine Clearance With eGFR and Cystatin C Based Cis-eGFR, Including Kinetic eGFR in the Immediate Post-transplant Period With Prompt Allograft Function

Abstract

IntroductioneGFR and KeGFR have not been compared, with urinary measured creatinine clearance (mCrCl) or serum Cystatin C eGFR, soon after kidney transplant with prompt primary function. The study aims to compare post-KTx, urinary mCrCl, and eGFRCysC with eGFR and KeGFR. MethodPost-KTx, urine was collected every 12 hours from 25 of the 34 consenting subjects to calculate mCrCl and compare with MDRD-4, Jelliffe eGFR, Cockcroft-Gault Creatinine-Clearance, and KeGFR by Chen and Brater formulae. Serum CysC levels were also measured in the last 14 subjects to compare with creatinine, mCrCl, and eGFRCysC. FindingsAt 12 to 96 hours post-KTx (n=25), mCrCl was 55.8% to 13.6% higher than MDRD-4 eGFR. The mean CysC level (n=14) was 58% to 14% lower than creatinine for up to 3.0 days post-KTx, with higher MDRD-4 eGFRCysC. Chen and Brater KeGFR were significantly lower than mCrCl and eGFR (figure-1B, table-1). Within three days post KTx, a 50% decrease in creatinine provided ≥ 50 mL/min CrCl in 90% of cases (mean mCrCl 61.7± 22.8). This difference was greater when the initial creatinine was higher with the rapid decrease in creatinine. Conclusion1) Post-KTx eGFR/KeGFR formulae underestimate mCrCl. 2) Serum CysC levels were lower than creatinine, corresponding higher eGFRCysC. 3) A 50% decrease from initial serum creatinine; mean mCrCl was 61.7±22.8 mL/min, and 90% of them have mCrCl > 50 mL/min. Post KTx, until creatinine is stabilized, recipients are often receiving subtherapeutic dosing of renally adjusted medications. More prospective studies are necessary, including radioisotope clearance.