V. Immediate processing of samples and cold chain: two indispensable elements for obtaining quality results

The interpretation of oxidative stress profiles must imperatively rely on particularly careful processing of blood samples. Most assays proposed for the evaluation of oxidative stress are very sensitive to sample preservation conditions (type of anticoagulant, temperature...). An example is the determination of reduced and oxidised glutathione. Figure 25 shows clearly how these two markers evolve if the analysis is carried out after storage of the blood for 1 hour or more at room temperature. In this case, the only way to have a good-quality, interpretable analysis is to place the blood immediately in contact with stabilisers and freeze it.

Figure 25 : Evolution of the GSH/GSSG ratio in blood samples kept at room temperature for 1 to 24 hours.

T0 : sample processed immediately after it was taken
Blue rectangle: reference interval

Generally speaking, these observations are valid also for all markers reflecting the presence of oxidative stress. Figure 26 shows that the conservation kinetics of oxidised lipoproteins fluctuates considerably, even in whole blood samples stored at +4°C. A reliable result is obtained only if the sample is centrifuged immediately and the plasma frozen at – 20°C.

Figure 26 : Evolution of the concentration of oxidised LDL (U/L) as a function of time

When scientists publish results on the evolution of plasma markers of oxidative stress (e.g. vitamin E), they are required to specify in the "Materials and Methods" section of the paper that the blood samples were immediately centrifuged and the plasma stored at –20°C until the marker of interest was analysed. Intent on respecting this directive scrupulously, PROBIOX SA has made available to users a highly detailed protocol for blood sample collection and processing and for sample transfer to the laboratory on dry ice and in suitable containers.