title: Long-term Stability of Urinary Biomarkers of Acute Kidney Injury in Children.
abstract: BACKGROUND
  Recent meta-analyses support the utility of urinary biomarkers for the diagnosis and prognosis of acute kidney injury. It is critical to establish optimal sample handling conditions for short-term processing and long-term urinary storage prior to widespread clinical deployment and meaningful use in prospective clinical trials.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  80 children (median age, 1.1 [IQR, 0.5-4.2] years) undergoing cardiac surgery with cardiopulmonary bypass at our center. 50% of patients had acute kidney injury (defined as ≥50% increase in serum creatinine from baseline).
  
  
  METHODS
  We tested the effect on biomarker concentrations of short-term urine storage in ambient, refrigerator, and freezer conditions. We also tested the effects of multiple freeze-thaw cycles, as well as prolonged storage for 5 years.
  
  
  RESULTS
  Urine concentrations of neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), and interleukin 18 (IL-18).
  
  
  METHODS
  All biomarkers were measured using commercially available kits.
  
  
  RESULTS
  All 3 biomarkers were stable in urine stored at 4°C for 24 hours, but showed significant degradation (5.6%-10.1% from baseline) when stored at 25°C. All 3 biomarkers showed only a small although significant decrease in concentration (0.77%-2.9% from baseline) after 3 freeze-thaw cycles. Similarly, all 3 biomarkers displayed only a small but significant decrease in concentration (0.84%-3.2%) after storage for 5 years.
  
  
  CONCLUSIONS
  Only the 3 most widely studied biomarkers were tested. Protease inhibitors were not evaluated.
  
  
  CONCLUSIONS
  Short-term storage of urine samples for measurement of NGAL, KIM-1, and IL-18 may be performed at 4°C for up to 24 hours, but not at room temperature. These urinary biomarkers are stable at -80°C for up to 5 years of storage. Our results are reassuring for the deployment of these assays as biomarkers in clinical practice, as well as in prospective clinical studies requiring long-term urine storage.
authors.affiliation: Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH.
authors.forename: Meredith P
authors.initials: MP
authors.lastname: Schuh
authors.affiliation: Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH.
authors.forename: Edward
authors.initials: E
authors.lastname: Nehus
authors.affiliation: Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH.
authors.forename: Qing
authors.initials: Q
authors.lastname: Ma
authors.affiliation: Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH.
authors.forename: Christopher
authors.initials: C
authors.lastname: Haffner
authors.affiliation: Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH.
authors.forename: Michael
authors.initials: M
authors.lastname: Bennett
authors.affiliation: Division of Pediatric Cardiology, Lucile Packard Children's Hospital, Stanford University, Palo Alto, CA.
authors.forename: Catherine D
authors.initials: CD
authors.lastname: Krawczeski
authors.affiliation: Division of Nephrology, Cincinnati Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH. Electronic address: prasad.devarajan@cchmc.org.
authors.forename: Prasad
authors.initials: P
authors.lastname: Devarajan
mesh_terms: D058186:Acute Kidney Injury / Q000652:urine*; D015415:Biomarkers / Q000652:urine; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011446:Prospective Studies; D055550:Protein Stability; D013997:Time Factors; D016482:Urinalysis
chemical_list: D015415:Biomarkers
keywords: Acute kidney injury (AKI); acute renal failure; biomarker stability; children; enzyme-linked immunosorbent assay (ELISA); freeze-thaw cycle; interleukin 18 (IL-18); kidney injury molecule 1 (KIM-1); neutrophil gelatinase-associated lipocalin (NGAL); pediatric patients; sample handling conditions; urinary biomarker; urine storage