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PLoS One. 2016 Oct 27;11(10):e0164832. doi: 10.1371/journal.pone.0164832. eCollection 2016.

Storage Time and Urine Biomarker Levels in the ASSESS-AKI Study.

Author information

Division of Nephrology, Department of Medicine, University of California, San Francisco, San Francisco, CA, United States of America.
Department of Medicine, Division of Nephrology and Hypertension, Vanderbilt University Medical Center, Nashville, TN, United States of America.
Department of Medicine, Division of Nephrology, Penn State College of Medicine, Hershey, PA, United States of America.
Kidney Research Institute, Department of Medicine, University of Washington, Seattle, WA, United States of America.
Division of Research, Kaiser Permanente Northern California, Oakland, CA, United States of America.
Division of Nephrology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, United States of America.
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.
Division of Kidney, Urologic, and Hematologic Diseases, NIDDK, NIH, Bethesda, MD, United States of America.
Department of Public Health Sciences, Penn State College of Medicine, Hershey, PA, United States of America.
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.



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.


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.


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.


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.

[Indexed for MEDLINE]
Free PMC Article

Conflict of interest statement

W. Brian Reeves is an Associate Editor of Kidney International, a journal of the International Society of Nephrology. Kathleen D. Liu and Chi-yuan Hsu had reagents donated for assays by Abbott Laboratories. Prasad Devarajan has patents submitted for the use of NGAL as a biomarker of kidney injury. T. Alp Ikizler is the Chair of the Medical Advisory Board for DSI, Inc, the Chair of the Scientific Advisory Board for Satellite Health, has received honoraria from Hospira for an advisory board, from Fresenius-Kabi for lecturing and for advisory boards, and from the American Board of Internal Medicine as a member of the Nephrology subspecialty committee. Jonathan Himmelfarb is the chair of the steering committee for a clinical trial for Thrasos, Inc. James Kaufman is the study director for a large randomized clinical trial for the Department of Veterans Affairs Cooperative Study Program. Because this is an ongoing study of human subjects with confidential data, the data cannot be shared at present because of patient confidentiality. At the end of the parent ASSESS-AKI study, a de-identified data set will be prepared in compliance with NIH guidelines and made publicly available. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

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