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

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...

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Published in	PloS one Vol. 11; no. 10; p. e0164832
Main Authors	Liu, Kathleen D., Siew, Edward D., Reeves, W. Brian, Himmelfarb, Jonathan, Go, Alan S., Hsu, Chi-yuan, Bennett, Michael R., Devarajan, Prasad, Ikizler, T. Alp, Kaufman, James S., Kimmel, Paul L., Chinchilli, Vernon M., Parikh, Chirag R.
Format	Journal Article
Language	English
Published	United States Public Library of Science 27.10.2016 Public Library of Science (PLoS)
Subjects	Acute Kidney Injury - urine Analysis Biology and Life Sciences Biomarkers Biomarkers - urine Blood diseases Chronic kidney failure Complications Diabetes Fatty acid-binding protein Fatty Acid-Binding Proteins - urine Fatty acids Female Gelatinase Hepatitis A Virus Cellular Receptor 1 - analysis Hospitalization Humans Hypertension Injury analysis Interleukin 18 Interleukin-18 - urine Interleukins Kidney diseases Kidneys Lipocalin Lipocalin-2 - urine Liver Male Medical research Medicine Medicine and Health Sciences Middle Aged Molecular chains Nephrology Neutrophils Protein binding Proteins Renal Insufficiency, Chronic - urine Research and Analysis Methods Statistical analysis Statistical methods Time Factors Urine Urine - chemistry Urine Specimen Collection - methods Urine Specimen Collection - statistics & numerical data Northern California New York San Francisco California California United States > US Nashville Tennessee
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Summary:	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.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14 content type line 23 Conceptualization: KDL EDS WBR JH ASG CYH MRB PD TAI JSK PLK VMC CRP. Formal analysis: VMC. Funding acquisition: JH ASG TAI PLK VMC CRP. Investigation: MRB PD. Methodology: KDL EDS WBR JH ASG CYH TAI JSK PLK VMC CRP. Resources: KDL EDS WBR JH ASG CYH MRB PD TAI JSK PLK VMC CRP. Writing – original draft: KDL VMC CRP. Writing – review & editing: KDL EDS WBR JH ASG CYH MRB PD TAI JSK PLK VMC CRP. Members of the ASSESS-AKI Study are listed in the Acknowledgments. Competing Interests: 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.
ISSN:	1932-6203 1932-6203
DOI:	10.1371/journal.pone.0164832