Prospective Comparison of Urinary Measured Creatinine Clearance With eGFR and Cystatin C Based Cis-eGFR, Including...

The estimated glomerular filtration rate (eGFR) and kinetic estimated glomerular filtration rate (KeGFR) have not been compared, with urinary measured creatinine clearance (mCrCl) or serum cystatin C (CysC) eGFR, soon after kidney transplantation (KTx) with prompt primary function. This study aims to compare post-KTx, urinary mCrCl, and eGFR CysC with eGFR and KeGFR.

Post-KTx, urine was collected every 12 hours from 25 of the 34 consenting subjects to calculate mCrCl and compare with Modification of Diet in Renal Disease (MDRD)-4, Jelliffe eGFR, Cockcroft-Gault creatinine clearance (CrCl), and KeGFR by Chen and Brater formulae. Serum CysC levels were also measured in the last 14 subjects to compare with creatinine, mCrCl, and eGFR CysC_. RESULTS: At 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 eGFR CysC. Chen and Brater KeGFR were significantly lower than mCrCl and eGFR (Fig 1B, Table 1). Within 3 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.

(1) Post-KTx eGFR/KeGFR formulae underestimated mCrCl. (2) Serum CysC levels were lower than creatinine, corresponding with higher eGFR CysC. (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.