Stability of carnitine, choline, betaine and TMAO in plasma of healthy volunteers. (A–D) Plasma samples of ten healthy volunteers were subjected to up to six freeze-thaw-cycles; freeze-thaw cycle No. 1 (blue), No. 2 (red), No. 3 (green), No. 4 (purple), No. 5 (orange), No. 6 (black). Data points are partly overlaid. Plasma concentrations were determined for (A) carnitine, (B) choline, (C) betaine, and (D) TMAO. (E–H) Plasma samples of three healthy volunteers (P1, P2 and P3) were stored for up to five days at room temperature. Plasma concentrations were determined on day 0, day 3 and day 5 for (E) carnitine, (F) choline, (G) betaine, and (H) TMAO. No statistically significant differences in plasma concentrations for carnitine, choline, betaine and TMAO were detected neither for the freeze-thaw-cycles nor for the stability test up to 5 days at room temperature using an ordinary one-way ANOVA.