title: 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 (1 g/kg protein) and participants 9 to 16 received a ProCel shake (1-1.5 g/kg protein).
  
  
  
  RR defined as the difference in stimulated versus baseline GFR.
  
  
  
  Baseline GFR (SD) in mL/minute/1.73 m2averaged 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/1.73 m2) 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.
authors.affiliation: University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.
authors.forename: Kyle E
authors.initials: KE
authors.lastname: Rodenbach
authors.affiliation: University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania.
authors.forename: Dana Y
authors.initials: DY
authors.lastname: Fuhrman
authors.affiliation: University of Rochester Medical Center, Rochester, New York.
authors.forename: Paula S
authors.initials: PS
authors.lastname: Maier
authors.affiliation: University of Rochester Medical Center, Rochester, New York. Electronic address: george_schwartz@urmc.rochester.edu.
authors.forename: George J
authors.initials: GJ
authors.lastname: Schwartz
mesh_terms: D015415:Biomarkers / Q000097:blood; D002927:Cimetidine / Q000008:administration & dosage*; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007472:Iohexol / Q000008:administration & dosage*; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D007674:Kidney Diseases / Q000188:drug therapy; D008297:Male; D055815:Young Adult
chemical_list: D015415:Biomarkers; C525030:CST3 protein, human; D055316:Cystatin C; D007472:Iohexol; D002927:Cimetidine; D003404:Creatinine