title: Storage Time and Urine Biomarker Levels in the ASSESS-AKI Study.
abstract: BACKGROUND
  Although stored urine samples are often used in biomarker studies focused on acute and chronic kidney disease, how storage time impacts biomarker levels is not well understood.
  
  
  METHODS
  866 subjects enrolled in the NIDDK-sponsored ASsessment, Serial Evaluation, and Subsequent Sequelae in Acute Kidney Injury (ASSESS-AKI) Study were included. Samples were processed under standard conditions and stored at -70°C until analyzed. Kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18 (IL-18), and liver fatty acid binding protein (L-FABP) were measured in urine samples collected during the index hospitalization or an outpatient visit 3 months later. Mixed effects models were used to determine the effect of storage time on biomarker levels and stratified by visit.
  
  
  RESULTS
  Median storage was 17.8 months (25-75% IQR 10.6-23.7) for samples from the index hospitalization and 14.6 months (IQR 7.3-20.4) for outpatient samples. In the mixed effects models, the only significant association between storage time and biomarker concentration was for KIM-1 in outpatient samples, where each month of storage was associated with a 1.7% decrease (95% CI -3% to -0.3%). There was no relationship between storage time and KIM-1 levels in samples from the index hospitalization.
  
  
  CONCLUSIONS
  There was no significant impact of storage time over a median of 18 months on urine KIM-1, NGAL, IL-18 or L-FABP in hospitalized samples; a statistically significant effect towards a decrease over time was noted for KIM-1 in outpatient samples. Additional studies are needed to determine whether longer periods of storage at -70°C systematically impact levels of these analytes.
authors: Division of Nephrology, Department of Medicine, University of California, San Francisco, San Francisco, CA, United States of America.
authors: Kathleen D
authors: KD
authors: Liu
authors: Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, TN, United States of America.
authors: Edward D
authors: ED
authors: Siew
authors: Department of Medicine, Division of Nephrology, Penn State College of Medicine, Hershey, PA, United States of America.
authors: W Brian
authors: WB
authors: Reeves
authors: Kidney Research Institute, Department of Medicine, University of Washington, Seattle, WA, United States of America.
authors: Jonathan
authors: J
authors: Himmelfarb
authors: Division of Research, Kaiser Permanente Northern California, Oakland, CA, United States of America.
authors: Alan S
authors: AS
authors: Go
authors: Division of Nephrology, Department of Medicine, University of California, San Francisco, San Francisco, CA, United States of America.|Division of Research, Kaiser Permanente Northern California, Oakland, CA, United States of America.
authors: Chi-Yuan
authors: CY
authors: Hsu
authors: Division of Nephrology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States of America.
authors: Michael R
authors: MR
authors: Bennett
authors: Division of Nephrology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States of America.
authors: Prasad
authors: P
authors: Devarajan
authors: Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, TN, United States of America.
authors: T Alp
authors: TA
authors: Ikizler
authors: Research Service and Renal Section, VA New York Harbor Healthcare System and New York University School of Medicine, New York, NY, United States of America.
authors: James S
authors: JS
authors: Kaufman
authors: Division of Kidney, Urologic, and Hematologic Diseases, NIDDK, NIH, Bethesda, MD, United States of America.
authors: Paul L
authors: PL
authors: Kimmel
authors: Department of Public Health Sciences, Penn State College of Medicine, Hershey, PA, United States of America.
authors: Vernon M
authors: VM
authors: Chinchilli
authors: Section of Nephrology, Department of Medicine, Yale University School of Medicine, New Haven, CT, United States of America.|Program of Applied Translational Research, Yale University School of Medicine, New Haven, CT, United States of America.
authors: Chirag R
authors: CR
authors: Parikh
mesh_terms: D058186:Acute Kidney Injury / Q000652:urine; D015415:Biomarkers / Q000652:urine; D050556:Fatty Acid-Binding Proteins / Q000652:urine; D005260:Female; D000072596:Hepatitis A Virus Cellular Receptor 1 / Q000032:analysis; D006801:Humans; D020382:Interleukin-18 / Q000652:urine; D000071068:Lipocalin-2 / Q000652:urine; D008297:Male; D008875:Middle Aged; D051436:Renal Insufficiency, Chronic / Q000652:urine; D013997:Time Factors; D014556:Urine / Q000737:chemistry*; D059349:Urine Specimen Collection / Q000379:methods* / Q000706:statistics & numerical data
chemical_list: D015415:Biomarkers; C493319:FABP1 protein, human; D050556:Fatty Acid-Binding Proteins; C491143:HAVCR1 protein, human; D000072596:Hepatitis A Virus Cellular Receptor 1; D020382:Interleukin-18; C489506:LCN2 protein, human; D000071068:Lipocalin-2