Quality assurance in the pre-analytical phase of human urine samples by 1H NMR spectroscopy

Metabolomic approaches investigate changes in metabolite profiles, which may reflect changes in metabolic pathways and provide information correlated with a specific biological process or pathophysiology. High-resolution 1H NMR spectroscopy is used to identify metabolites in biofluids and tissue samples qualitatively and quantitatively. This pre-analytical study evaluated the effects of storage time and temperature on 1H NMR spectra from human urine in two settings. Firstly, to evaluate short time effects probably due to acute delay in sample handling and secondly, the effect of prolonged storage up to one month to find markers of sample miss-handling. A number of statistical procedures were used to assess the differences between samples stored under different conditions, including Projection to Latent Structure Discriminant Analysis (PLS-DA), non-parametric testing as well as mixed effect linear regression analysis. The results indicate that human urine samples can be stored at 10 °C for 24 h or at −80 °C for 1 month, as no relevant changes in 1H NMR fingerprints were observed during these time periods and temperature conditions. However, some metabolites most likely of microbial origin showed alterations during prolonged storage but without facilitating classification. In conclusion, the presented protocol for urine sample handling and semi-automatic metabolite quantification is suitable for large-scale epidemiological studies.