title: Glomerular filtration rate measured by iohexol clearance: A comparison of venous samples and capillary blood spots.
abstract: BACKGROUND
  Glomerular filtration rate (GFR) measured by iohexol clearance using venous samples is widely used. Capillary sampling on filter paper is easier to perform, may be less painful and spares the blood volume. The purpose of the study was to validate a blood spot method for measuring GFR in children aged 6 years or younger suffering from chronic kidney disease (CKD).
  
  
  METHODS
  We examined 32 children with CKD, median age (range) 3.0 (0.3-6.2) years. Seven venous samples (10, 30/60, 120, 180, 210, 240, 300 min) were collected and GFR based on all samples was calculated for reference. Following injection of iohexol, blood spots were collected at 120, 180, 210 and 240 min and compared to the reference iohexol clearance.
  
  
  RESULTS
  Median (range) reference GFR was 65 (6-122) mL/min/1.73 m(2). The 2, 3 and 4-point blood spot GFR were highly correlated to the reference GFR (r = 0.947, 0.945, 0.937). The mean relative bias between 2-point blood spot and reference GFR was 7.2%, and only 2.3% in the patients with reference GFR < 60 mL/min/1.73 m(2). The diagnostic accuracy for 2-point blood spot was: 87.5% and 96.9% within ± 15% (P15) and ± 30% (P30) of the reference GFR respectively. In patients with GFR < 60 mL/min/1.73 m(2), both P15 and P30 were 100%.
  
  
  CONCLUSIONS
  GFR calculation based on blood spot iohexol measurement is an alternative method to traditional venous iohexol measurement in children. Our study demonstrates strong agreement between the blood spot and the venous GFR with acceptable bias, precision and diagnostic accuracy, especially in patients with GFR < 60 mL/min/1.73 m(2).
authors.affiliation: a Department of Medical Biochemistry , Oslo University Hospital , Norway.
authors.forename: Cathrin Lytomt
authors.initials: CL
authors.lastname: Salvador
authors.affiliation: b Department of Pediatrics , Haukeland University Hospital , Bergen , Norway.|c Department of Clinical Medicine , University of Bergen , Norway.
authors.forename: Camilla
authors.initials: C
authors.lastname: Tøndel
authors.affiliation: a Department of Medical Biochemistry , Oslo University Hospital , Norway.|d Institute of Clinical Medicine, University of Oslo , Norway.
authors.forename: Lars
authors.initials: L
authors.lastname: Mørkrid
authors.affiliation: e Department of Pediatrics , Oslo University Hospital , Norway.
authors.forename: Anna
authors.initials: A
authors.lastname: Bjerre
authors.affiliation: f Laboratory of Clinical Biochemistry, Haukeland University Hospital , Bergen , Norway.|g Department of Clinical Science , University of Bergen , Norway.
authors.forename: Atle
authors.initials: A
authors.lastname: Brun
authors.affiliation: f Laboratory of Clinical Biochemistry, Haukeland University Hospital , Bergen , Norway.|g Department of Clinical Science , University of Bergen , Norway.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Bolann
authors.affiliation: b Department of Pediatrics , Haukeland University Hospital , Bergen , Norway.
authors.forename: Damien
authors.initials: D
authors.lastname: Brackman
authors.affiliation: h Department of Pharmacology , Oslo University Hospital , Norway.|i School of Pharmacy, University of Oslo , Norway.
authors.forename: Stein
authors.initials: S
authors.lastname: Bergan
mesh_terms: D002648:Child; D002675:Child, Preschool; D003287:Contrast Media / Q000378:metabolism* / Q000493:pharmacokinetics; D059788:Dried Blood Spot Testing; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007223:Infant; D007472:Iohexol / Q000378:metabolism* / Q000493:pharmacokinetics; D008297:Male; D008657:Metabolic Clearance Rate; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000175:diagnosis / Q000503:physiopathology
chemical_list: D003287:Contrast Media; D007472:Iohexol
keywords: Child; chromatography; dried blood spot testing; high pressure liquid; kidney diseases; kidney function tests