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Am J Kidney Dis. 2014 Apr;63(4):567-72. doi: 10.1053/j.ajkd.2013.09.013. Epub 2013 Nov 5.

Urine stability studies for novel biomarkers of acute kidney injury.

Author information

  • 1Section of Nephrology, Department of Medicine, Yale University School of Medicine, New Haven, CT; Program of Applied Translational Research, Yale University School of Medicine, New Haven, CT. Electronic address: chirag.parikh@yale.edu.
  • 2Section of Nephrology, Department of Medicine, Yale University School of Medicine, New Haven, CT; Program of Applied Translational Research, Yale University School of Medicine, New Haven, CT.
  • 3Department of Public Health Sciences, Penn State College of Medicine, Hershey, PA.
  • 4Division of Nephrology, Department of Medicine, University of California, San Francisco, CA.
  • 5Division of Nephrology, Department of Medicine, University of California, San Francisco, CA; Division of Research, Kaiser Permanente of Northern California, Oakland, CA.
  • 6Department of Medicine, Division of Nephrology, Penn State College of Medicine, Hershey, PA.
  • 7Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center, Cincinnati, OH.
  • 8Division of Kidney, Urologic, and Hematologic Diseases, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD.
  • 9Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, TN.

Abstract

BACKGROUND:

The study of novel urinary biomarkers of acute kidney injury has expanded exponentially. Effective interpretation of data and meaningful comparisons between studies require awareness of factors that can adversely affect measurement. We examined how variations in short-term storage and processing might affect the measurement of urine biomarkers.

STUDY DESIGN:

Cross-sectional prospective.

SETTING & PARTICIPANTS:

Hospitalized patients from 2 sites: Yale New Haven Hospital (n=50) and University of California, San Francisco Medical Center (n=36).

PREDICTORS:

We tested the impact of 3 urine processing conditions on these biomarkers: (1) centrifugation and storage at 4°C for 48 hours before freezing at -80°C, (2) centrifugation and storage at 25°C for 48 hours before freezing at -80°C, and (3) uncentrifuged samples immediately frozen at -80°C.

OUTCOMES:

Urine concentrations of 5 biomarkers: neutrophil gelatinase-associated lipocalin (NGAL), interleukin 18 (IL-18), kidney injury molecule 1 (KIM-1), liver-type fatty acid-binding protein (L-FABP), and cystatin C.

MEASUREMENTS:

We measured urine biomarkers by established enzyme-linked immunosorbent assay methods. Biomarker values were log-transformed, and agreement with a reference standard of immediate centrifugation and storage at -80°C was compared using concordance correlation coefficients (CCCs).

RESULTS:

Neither storing samples at 4°C for 48 hours nor centrifugation had a significant effect on measured levels, with CCCs higher than 0.9 for all biomarkers tested. For samples stored at 25°C for 48 hours, excellent CCC values (>0.9) also were noted between the test sample and the reference standard for NGAL, cystatin C, L-FABP and KIM-1. However, the CCC for IL-18 between samples stored at 25°C for 48 hours and the reference standard was 0.81 (95% CI, 0.66-0.96).

LIMITATIONS:

No comparisons to fresh, unfrozen samples; no evaluation of the effect of protease inhibitors.

CONCLUSIONS:

All candidate markers tested using the specified assays showed high stability with both short-term storage at 4°C and without centrifugation prior to freezing. For optimal fidelity, urine for IL-18 measurement should not be stored at 25°C before long-term storage or analysis.

Copyright © 2014 National Kidney Foundation, Inc. All rights reserved.

KEYWORDS:

Proteins; acute kidney injury (AKI); acute renal failure (ARF); biospecimen handling; concordance; handling; protein stability; storage; urine biomarker

PMID:
24200462
[PubMed - indexed for MEDLINE]
PMCID:
PMC3969397
Free PMC Article
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