Figure 4.

Effect of sample preparation on relative sphingosine 1-phosphate (A,B) and sphinganine 1-phosphate (C,D) levels in human blood samples. (A,C) Plasma was directly separated from blood (EDTA as anticoagulant) by 5 min centrifugation (4 °C) at 550× g, 5800× g or 16,200× g. (B,D) Plasma was directly separated from blood (EDTA as anticoagulant) as described in the Material and Methods section. Thereafter, plasma samples were either snap frozen in liquid nitrogen or frozen at −20 °C or −80 °C. Plasma separated at 550× g (A,C) and snap frozen (B,D) served as the respective controls (100%). All plasma samples were stored at −80 °C until LC-MS/MS analysis. Data are shown as mean (in %) ± SD (n = 4). * p < 0.05, *** p < 0.001.