Statistical analyses
Independent sample t-tests were used for parametrically distributed data on interval scale level. For non-parametric data the Mann-Whitney U test was used to compare groups. Variables on nominal levels were tested by Fisher´s exact test. Some of the variables were skewed and therefore transformed to their natural logarithm (ln) before analyses with parametric tests could be conducted. Those analytes that had more than 10% of values with LLOQ were transformed into binary variables, where 0 denoted “under LLOQ” and 1 denoted “over LLOQ”. Spearman rank correlations (R