title: Discordance Between Iothalamate and Iohexol Urinary Clearances.
abstract: BACKGROUND
  Iothalamate and iohexol are contrast agents that have supplanted inulin for the measurement of glomerular filtration rate (GFR) in clinical practice. Previous studies have noted possible differences in renal handling of these 2 agents, but clarity about the differences has been lacking.
  
  
  METHODS
  Study of diagnostic test accuracy.
  
  
  METHODS
  150 participants with a wide range of GFRs were studied in an outpatient clinical laboratory facility.
  
  
  METHODS
  Simultaneous urinary clearances of iothalamate, iohexol, and creatinine.
  
  
  METHODS
  None.
  
  
  RESULTS
  Relative differences between the urinary clearances. Iohexol and iothalamate in plasma and urine were assayed concurrently by a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay.
  
  
  RESULTS
  Mean iohexol, iothalamate, and creatinine clearances were 52±28 (SD), 60±34, and 74±40 mL/min/1.73 m(2), respectively. The proportional bias of iohexol to iothalamate urinary clearance was 0.85 (95% CI, 0.83-0.88) and was proportional across the GFR range. The mean proportional bias of iohexol clearance compared with creatinine clearance is 1.27 (95% CI, 1.20-1.34), whereas that of iothalamate clearance compared with creatinine clearance is 1.09 (95% CI, 1.03-1.15).
  
  
  CONCLUSIONS
  Lack of reference standard.
  
  
  CONCLUSIONS
  This study reveals a significant and consistent difference between urinary clearances of iothalamate and iohexol. Comparison of studies reporting renal clearance measurements using iohexol versus iothalamate must account for this observed bias.
authors.affiliation: Department of Laboratory Medicine, University of Minnesota, Rochester, MN.
authors.forename: Jesse C
authors.initials: JC
authors.lastname: Seegmiller
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN.
authors.forename: Bradley E
authors.initials: BE
authors.lastname: Burns
authors.affiliation: Division of Nephrology and Hypertension, Department of Internal Medicine, Mayo Clinic, Rochester, MN.
authors.forename: Carrie A
authors.initials: CA
authors.lastname: Schinstock
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN; Division of Nephrology and Hypertension, Department of Internal Medicine, Mayo Clinic, Rochester, MN.
authors.forename: John C
authors.initials: JC
authors.lastname: Lieske
authors.affiliation: Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN; Division of Nephrology and Hypertension, Department of Internal Medicine, Mayo Clinic, Rochester, MN. Electronic address: larson.timothy@mayo.edu.
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Larson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002853:Chromatography, Liquid; D005260:Female; D005919:Glomerular Filtration Rate; D006403:Hematologic Tests; D006801:Humans; D007472:Iohexol / Q000032:analysis*; D007483:Iothalamic Acid / Q000032:analysis*; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry; D016482:Urinalysis; D055815:Young Adult
chemical_list: D007483:Iothalamic Acid; D007472:Iohexol
keywords: Glomerular filtration rate (GFR); exogenous filtration marker; iohexol; iothalamate; kidney function; liquid chromatography tandem mass spectrometry (LC-MS/MS); measured GFR (mGFR); plasma; renal clearance; urine