title: Iohexol plasma clearance in children: validation of multiple formulas and two-point sampling times.
abstract: In children, estimated glomerular filtration rate (eGFR) methods are hampered by inaccuracy, hence there is an obvious need for safe, simplified, and accurate measured GFR (mGFR) methods. The aim of this study was to evaluate different formulas and determine the optimal sampling points for calculating mGFR based on iohexol clearance measurements on blood samples drawn at two time points (GFR2p).
  
  
  
  The GFR of 96 children with different stages of chronic kidney disease (CKD) (median age 9.2 years, range 3 months to 17.5 years) was determined using the iohexol plasma clearance, with blood sampling at seven time points within 5 h (GFR7p) as the reference method. Median GFR7p was 65.9 (range 6.3-153) mL/min/1.73 m2. The performance of seven different formulas with early and late normalization to body surface area (BSA) was validated against the reference.
  
  
  
  The highest percentage (95.8 %) of GFR2p within 10 % of the reference was calculated using the formula of Jødal and Brøchner-Mortensen (JBM) from 2009, with sampling at 2 and 5 h. Normalization to BSA before correction of the distribution phase improved the performance of the original Brøchner-Mortensen method from 1972; P10 of 92.7 % compared to P10 of 82.3 % with late normalization, and a similar result was obtained with other formulas.
  
  
  
  GFR2p performed well across a wide spectrum of GFR levels with the JBM formula. Several other formulas tested performed well provided that early BSA normalization was performed. Blood sampling at 2 and 5 h is recommended for an optimal GFR2p assessment.
authors.affiliation: Department of Pediatrics, Haukeland University Hospital, N-5021, Bergen, Norway. camilla.tondel@helse-bergen.no.|Department of Clinical Medicine, University of Bergen, Bergen, Norway. camilla.tondel@helse-bergen.no.
authors.forename: Camilla
authors.initials: C
authors.lastname: Tøndel
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway.|Laboratory for Clinical Biochemistry, Haukeland University Hospital, Bergen, Norway.
authors.forename: Bjørn
authors.initials: B
authors.lastname: Bolann
authors.affiliation: Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Cathrin Lytomt
authors.initials: CL
authors.lastname: Salvador
authors.affiliation: Department of Pediatrics, Oslo University Hospital, Oslo, Norway.
authors.forename: Damien
authors.initials: D
authors.lastname: Brackman
authors.affiliation: Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Anna
authors.initials: A
authors.lastname: Bjerre
authors.affiliation: Department of Clinical Medicine, University of Bergen, Bergen, Norway.|Department of Medicine, Haukeland University Hospital, Bergen, Norway.
authors.forename: Einar
authors.initials: E
authors.lastname: Svarstad
authors.affiliation: Department of Clinical Science, University of Bergen, Bergen, Norway.|Laboratory for Clinical Biochemistry, Haukeland University Hospital, Bergen, Norway.
authors.forename: Atle
authors.initials: A
authors.lastname: Brun
mesh_terms: D000293:Adolescent; D001830:Body Surface Area; D002648:Child; D002675:Child, Preschool; D003287:Contrast Media; D005260:Female; D006801:Humans; D007223:Infant; D007472:Iohexol / Q000008:administration & dosage / Q000032:analysis*; D007677:Kidney Function Tests / Q000379:methods*; D008297:Male; D012016:Reference Values; D051436:Renal Insufficiency, Chronic / Q000097:blood*; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods; D013997:Time Factors
chemical_list: D003287:Contrast Media; D007472:Iohexol
keywords: Child; Chronic kidney disease; Glomerular filtration rate; Method; Renal function