title: Iohexol plasma clearance measurement in older adults with chronic kidney disease-sampling time matters.
abstract: BACKGROUND
  Accurate and precise measurement of GFR is important for patients with chronic kidney disease (CKD). Sampling time of exogenous filtration markers may have great impact on measured GFR (mGFR) results, but there is still uncertainty about optimal timing of plasma clearance measurement in patients with advanced CKD, for whom 24-h measurement is recommended. This satellite project of the Berlin Initiative Study evaluates whether 24-h iohexol plasma clearance reveals a clinically relevant difference compared with 5-h measurement in older adults.
  
  
  METHODS
  In 104 participants with a mean age of 79 years and diagnosed CKD, we performed standard GFR measurement over 5 h (mGFR300) using iohexol plasma concentrations at 120, 180, 240 and 300 min after injection. With an additional sample at 1440 min, we assessed 24-h GFR measurement (mGFR1440). Study design was cross-sectional. Calculation of mGFR was conducted with a one compartment model using the Brochner-Mortensen equation to calculate the fast component. mGFR values were compared with estimated GFR values (MDRD, CKD-EPI, BIS1, Revised Lund-Malmö and Cockcroft-Gault).
  
  
  RESULTS
  In all 104 subjects, mGFR1440 was lower than mGFR300 (23 ± 8 versus 29 ± 9 mL/min/1.73 m(2), mean ± SD; P < 0.001). mGFR1440 was highly correlated with mGFR300 (r = 0.9). The mean absolute difference mGFR300 - mGFR1440 was 5.9 mL/min/1.73 m(2) corresponding to a mean percentage difference of 29%. In individuals with eGFRCKD-EPI ≤ 30 mL/min/1.73 m(2), percentage difference of mGFR300 and mGFR1440 was even higher (35%). To predict mGFR1440 from mGFR300, we developed the correction formula: mGFR1440 = -2.175 + 0.871 × mGFR300 (1-fold standard error of estimate: ±2.3 mL/min/1.73 m(2)). The GFR estimating equation with the best accuracy and precision compared with mGFR300 and mGFR1440 was the Revised Lund Malmö.
  
  
  CONCLUSIONS
  In elderly CKD patients, measurement of iohexol clearance up to 5 h leads to a clinically relevant overestimation of GFR compared with 24-h measurement. In clinical care, this effect should be bore in mind especially for patients with considerably reduced GFR levels. A new correction formula has been developed to predict mGFR1440 from mGFR300. For accurate GFR estimates in elderly CKD patients, we recommend the Revised Lund Malmö equation.
authors.affiliation: Division of Nephrology, Charité University Medicine, Campus Virchow, Berlin, Germany.
authors.forename: Natalie
authors.initials: N
authors.lastname: Ebert
authors.affiliation: Division of Nephrology, Charité University Medicine, Campus Virchow, Berlin, Germany.
authors.forename: Amina
authors.initials: A
authors.lastname: Loesment
authors.affiliation: Institute of Clinical Epidemiology and Medical Biostatistics, University of Tübingen, Tübingen, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Martus
authors.affiliation: Institute of Biostatistics and Clinical Epidemiology, Charité, Berlin, Germany.
authors.forename: Olga
authors.initials: O
authors.lastname: Jakob
authors.affiliation: Division of Nephrology, Charité University Medicine, Campus Mitte, Berlin, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Gaedeke
authors.affiliation: Department of Nephrology, Vivantes Klinikum im Friedrichshain, Berlin, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Kuhlmann
authors.affiliation: Limbach Laboratory, Heidelberg, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Bartel
authors.affiliation: Division of Nephrology, Charité University Medicine Campus Benjamin Franklin, Berlin, Germany.
authors.forename: Mirjam
authors.initials: M
authors.lastname: Schuchardt
authors.affiliation: Division of Nephrology, Charité University Medicine Campus Benjamin Franklin, Berlin, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Tölle
authors.affiliation: Division of Nephrology, Charité University Medicine Campus Benjamin Franklin, Berlin, Germany.
authors.forename: Tao
authors.initials: T
authors.lastname: Huang
authors.affiliation: Division of Nephrology, Charité University Medicine Campus Benjamin Franklin, Berlin, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: van der Giet
authors.affiliation: Division of Nephrology, Charité University Medicine, Campus Virchow, Berlin, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Schaeffner
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood*; D015331:Cohort Studies; D003287:Contrast Media / Q000378:metabolism / Q000493:pharmacokinetics*; D003404:Creatinine / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007472:Iohexol / Q000378:metabolism / Q000493:pharmacokinetics*; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D051436:Renal Insufficiency, Chronic / Q000378:metabolism* / Q000503:physiopathology; D013048:Specimen Handling; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D015415:Biomarkers; D003287:Contrast Media; D007472:Iohexol; D003404:Creatinine
keywords: 24 hours iohexol clearance; GFR measurement protocol; elderly; measured GFR; reduced renal function