title: Stability of targeted metabolite profiles of urine samples under different storage conditions.
abstract: BACKGROUND
  Few studies have investigated the influence of storage conditions on urine samples and none of them used targeted mass spectrometry (MS).
  
  
  OBJECTIVE
  We investigated the stability of metabolite profiles in urine samples under different storage conditions using targeted metabolomics.
  
  
  METHODS
  Pooled, fasting urine samples were collected and stored at -80 °C (biobank standard), -20 °C (freezer), 4 °C (fridge), ~9 °C (cool pack), and ~20 °C (room temperature) for 0, 2, 8 and 24 h. Metabolite concentrations were quantified with MS using the AbsoluteIDQ™ p150 assay. We used the Welch-Satterthwaite-test to compare the concentrations of each metabolite. Mixed effects linear regression was used to assess the influence of the interaction of storage time and temperature.
  
  
  RESULTS
  The concentrations of 63 investigated metabolites were stable at -20 and 4 °C for up to 24 h when compared to samples immediately stored at -80 °C. When stored at ~9 °C for 24 h, few amino acids (Arg, Val and Leu/Ile) significantly decreased by 40% in concentration (P< 7.9E-04); for an additional three metabolites (Ser, Met, Hexose H1) when stored at ~20 °C reduced up to 60% in concentrations. The concentrations of four more metabolites (Glu, Phe, Pro, and Thr) were found to be significantly influenced when considering the interaction between exposure time and temperature.
  
  
  CONCLUSIONS
  Our findings indicate that 78% of quantified metabolites were stable for all examined storage conditions. Particularly, some amino acid concentrations were sensitive to changes after prolonged storage at room temperature. Shipping or storing urine samples on cool packs or at room temperature for more than 8 h and multiple numbers of freeze and thaw cycles should be avoided.
authors.affiliation: Research Unit of Molecular Epidemiology, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; Institute of Epidemiology II, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Rotter
authors.affiliation: Research Unit of Molecular Epidemiology, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; Institute of Epidemiology II, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Brandmaier
authors.affiliation: Genome Analysis Center, Institute of Experimental Genetics, Helmholtz Zentrum München, German Research Center for Environmental Health, 85764 München-Neuherberg, Germany.
authors.forename: Cornelia
authors.initials: C
authors.lastname: Prehn
authors.affiliation: Research Unit of Molecular Epidemiology, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; Institute of Epidemiology II, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Adam
authors.affiliation: Institute for Prevention and Occupational Medicine of the German Social Accident Insurance, Institute of the Ruhr University Bochum (IPA), 44789 Bochum, Germany.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Rabstein
authors.affiliation: Institute for Prevention and Occupational Medicine of the German Social Accident Insurance, Institute of the Ruhr University Bochum (IPA), 44789 Bochum, Germany.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Gawrych
authors.affiliation: Institute for Prevention and Occupational Medicine of the German Social Accident Insurance, Institute of the Ruhr University Bochum (IPA), 44789 Bochum, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Brüning
authors.affiliation: Research Unit of Molecular Epidemiology, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; Hannover Unified Biobank, Hannover Medical School, 30625 Hannover, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Illig
authors.affiliation: Institute of Diabetes and Regeneration Research, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; Institute of Stem Cell Research, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; German Center for Diabetes Research (DZD), 85764 München-Neuherberg, Germany.
authors.forename: Heiko
authors.initials: H
authors.lastname: Lickert
authors.affiliation: Genome Analysis Center, Institute of Experimental Genetics, Helmholtz Zentrum München, German Research Center for Environmental Health, 85764 München-Neuherberg, Germany ; German Center for Diabetes Research (DZD), 85764 München-Neuherberg, Germany ; Experimental Genetics, Center of Life and Food Sciences Weihenstephan, Technische Universität München, 85354 Freising-Weihenstephan, Germany.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Adamski
authors.affiliation: Research Unit of Molecular Epidemiology, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; Institute of Epidemiology II, Helmholtz Zentrum München, 85764 München-Neuherberg, Germany ; German Center for Diabetes Research (DZD), 85764 München-Neuherberg, Germany.
authors.forename: Rui
authors.initials: R
authors.lastname: Wang-Sattler
keywords: Amino acids; Pre-analytics; Storage conditions; Targeted metabolomics; Urine