title: Determining 'true' glomerular filtration rate in healthy adults using infusion of inulin and comparing it with values obtained using other clearance techniques or prediction equations.
abstract: OBJECTIVE
  To determine 'true' glomerular filtration rate (GFR) in healthy adults as renal clearance following infusion of inulin, and compare that result with those obtained using other markers and clearance techniques and with estimations of GFR using creatinine-based prediction equations.
  
  
  METHODS
  Twenty healthy volunteers (11 females) with a median age of 27 years (range 19-36 years) received bolus doses of inulin and iohexol i.v. and 16 blood samples were taken after injection. Then, inulin and iohexol were infused to give stable plasma concentrations and blood and urine samples were collected. Residual bladder volume was estimated using ultrasound scanning. Plasma and urine concentrations of inulin and iohexol were determined using chromatography and resorcinol methods, respectively. Different methods of GFR determination were compared as well as four formulae for GFR estimation based on serum creatinine.
  
  
  RESULTS
  'True' GFR, i.e. renal clearance of inulin during its infusion, was a median of 117 ml/min/1.73 m2 (inter-quartile range 106-129 ml/min/1.73 m2). Similar values of GFR were obtained with renal clearance of iohexol during its infusion and also with plasma (body) clearance of inulin or iohexol following bolus injections and using 16 or five plasma samples. Endogenous creatinine clearance was higher (p<0.001) than true GFR (median 23 ml/min/1.73 m2). Plasma clearance of iohexol and inulin based on their concentrations in four blood samples underestimated their renal clearance considerably. All four creatinine-based formulae markedly underestimated renal inulin clearance.
  
  
  CONCLUSIONS
  Plasma and renal clearance of iohexol and inulin were similar in healthy adults. Underestimation of GFR was noted when plasma clearance of iohexol and inulin was based on four but not five or more blood samples. Some prediction equations underestimate true GFR to such an extent that caution must be taken when using them to evaluate normal or high GFR values.
authors.affiliation: Department of Nephrology and Transplantation, Malmö University Hospital, Malmö, Sweden. pog.sterner@telia.com
authors.forename: G
authors.initials: G
authors.lastname: Sterner
authors.forename: B
authors.initials: B
authors.lastname: Frennby
authors.forename: S
authors.initials: S
authors.lastname: Mansson
authors.forename: U
authors.initials: U
authors.lastname: Nyman
authors.forename: D
authors.initials: D
authors.lastname: Van Westen
authors.forename: T
authors.initials: T
authors.lastname: Almén
mesh_terms: D000328:Adult; D002851:Chromatography, High Pressure Liquid; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007444:Inulin / Q000378:metabolism*; D007472:Iohexol / Q000378:metabolism*; D007677:Kidney Function Tests / Q000379:methods; D008297:Male
chemical_list: D007472:Iohexol; D007444:Inulin