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

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


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.

Conclusion: 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.

MeSH terms

  • Acute Kidney Injury / urine
  • Biomarkers / urine
  • Fatty Acid-Binding Proteins / urine
  • Female
  • Hepatitis A Virus Cellular Receptor 1 / analysis
  • Humans
  • Interleukin-18 / urine
  • Lipocalin-2 / urine
  • Male
  • Middle Aged
  • Renal Insufficiency, Chronic / urine
  • Time Factors
  • Urine / chemistry*
  • Urine Specimen Collection / methods*
  • Urine Specimen Collection / statistics & numerical data


  • Biomarkers
  • FABP1 protein, human
  • Fatty Acid-Binding Proteins
  • HAVCR1 protein, human
  • Hepatitis A Virus Cellular Receptor 1
  • Interleukin-18
  • LCN2 protein, human
  • Lipocalin-2