title: Comparison of a simple and a standard method for inulin renal clearance.
abstract: BACKGROUND
  The standard method of renal inulin clearance consists of three sets of 30-min clearances. We previously proposed a simple method with a single urine collection for 1 h and two blood samples. In this study, we compared the two methods.
  
  
  METHODS
  The study involved 112 individuals. Three sets of 30-min urine sample collections were started 45 min after inulin infusion , and serum concentrations were measured at the midpoint (60, 90, 120 min) of each clearance period. The mean of the three (Cin-ST) or average of the first two (Cin-ST2) clearances was used for the standard method. Clearance calculated by the simple method (Cin-S) combined the first two collections and the mean of serum concentrations at the beginning (45 min) and end (105 min) of the clearance period. Clearance was also calculated by estimated area under the plasma concentration curve from 45 to 105 min (Cin-A) as a more reliable value.
  
  
  RESULTS
  Cin-S correlated highly with Cin-ST (r = 0.992). Bland-Altman plot indicated that Cin-S was lower than Cin-ST at the same rate in all glomerular filtration rate (GFR) ranges. Total Cin-S of all patients was significantly lower (5.9%, 4.8%, and 3.6%) than Cin-ST, Cin-ST2, and Cin-A, respectively. Cin-ST2 was 1.3% higher than Cin-A. The change in serum inulin concentration by time from 45 to 105 min was not linear but concave. This led to the underestimation of clearance by the simple method.
  
  
  CONCLUSIONS
  The simple method of renal inulin clearance gives slightly lower results than the standard method. The difference was small, indicating the simple method is accurate enough for use in clinical practice.
authors.affiliation: Department of Functional Diagnostic Science, Osaka University Graduate School of Medicine, Suita, Osaka, 565-0871, Japan. horio@sahs.med.osaka-u.ac.jp
authors.forename: Masaru
authors.initials: M
authors.lastname: Horio
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Yasuda
authors.forename: Shiro
authors.initials: S
authors.lastname: Takahara
authors.forename: Enyu
authors.initials: E
authors.lastname: Imai
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Seiichi
authors.initials: S
authors.lastname: Matsuo
mesh_terms: D000328:Adult; D000368:Aged; D006801:Humans; D007444:Inulin / Q000097:blood / Q000652:urine; D007668:Kidney / Q000378:metabolism*; D007677:Kidney Function Tests / Q000379:methods / Q000592:standards; D008657:Metabolic Clearance Rate / Q000502:physiology*; D008875:Middle Aged
chemical_list: D007444:Inulin