Renal Response to a Protein Load in Healthy Young Adults as Determined by Iohexol Infusion Clearance, Cimetidine-Inhibited Creatinine Clearance, and Cystatin C Estimated Glomerular Filtration Rate

Abstract

Renal reserve (RR) measures the increase in glomerular filtration rate (GFR) in response to a protein load; lack of RR could indicate subclinical kidney disease but such a test is not routinely used in clinical practice. The purpose of this study was to compare a meat versus liquid protein load in a cystatin C-based (Cys-C) RR test using cimetidine-inhibited creatinine clearance (Cr Cl) and iohexol infusion clearance (Io Cl) for validation. The design was cross-sectional analysis and the setting was a Clinical Research Center. Participants (N=16), mean (standard deviation [SD]) age 22 (2) years, had normal health and blood pressure without proteinuria. Participants 1 to 8 received a beef burger (1g/kg protein) and participants 9 to 16 received a ProCel shake (1-1.5g/kg protein). RR defined as the difference in stimulated versus baseline GFR. Baseline GFR (SD) in mL/minute/1.73m2 averaged 103.0 (15.6) for Cr Cl, 94.8 (7.9) for Io Cl, and 117.0 (6.0) for Cys-C estimated GFR (eGFR). Mean RR (SD) for the burger group (N=8, mL/minute/1.73m2) was 16.6 (12.3) for Cr Cl (P=.006); 7.2 (3.7) for Io Cl (P<.001), and 4.9 (2.6) for Cys-C eGFR (P=.001). Mean RR for the shake group (N=8) was 15.8 (5.8) for Cr Cl (P<.001), 10.1 (7.8) for Io Cl (P=.008), and 2.4 (2.9) for Cys-C eGFR (P=.05). Protein loading stimulates Io Cl and Cr Cl after a beef or milk-based protein load. The change in Cys-C eGFR is significant but smaller for the shake and burger group, which may be due to the dilutional effect of water loading or the length of Cys-C half-life in the blood.