Prolonged incubation of blood prior to plasma preparation can significantly influence the quality of the resulting data. Different markers for this pre-clinical variability have been proposed over the years but with limited success. In this study we explored the usefulness of glutathione (GSH) status, namely ratio of reduced to oxidized glutathione (GSH/GSSG), as potential marker of plasma preparation delay. For that purpose, blood from 20 healthy volunteers was collected into tubes with a cysteine quencher (N-ethylmaleimide; NEM) for GSH stabilization. Plasma preparation was delayed at room temperature for up to 3 hours and every hour, a plasma sample was prepared and the GSH/GSSG ratio measured. We report that over the course of the investigation, plasma concentrations of both GSH and GSSG increased linearly (R2 = 0.99 and 0.98, respectively). Since GSH increased at a much faster rate compared to GSSG, the GSH/GSSG ratio also increased linearly in a time dependent manner (R2 = 0.99). As GSH is an intracellular antioxidant, we speculated that this might stem from ongoing blood hemolysis, which was confirmed by the time dependent rise in lactate dehydrogenase (LDH) activity in the plasma samples. Moreover, we demonstrate that the addition of the thiol alkylating reagent NEM directly to the blood tubes does not seem to influence downstream analysis of clinical parameters. In conclusion we propose that the glutathione status could be used as an indicator of the centrifugation delay prior to plasma preparation.
PLASMA GLUTATHIONE IS A DETERMINANT OF NEUTROPHILS' COUNTING IN PATIENTS TAKING CLOZAPINE (CLZ)