Methods compared for determining glutathione peroxidase activity in blood.

We compared four methods for determination of glutathione peroxidase (EC 1.11.1.9) activity, using blood samples from 52 healthy volunteers. Two methods depended on direct assay of the amount of glutathione remaining at specific time intervals; the two indirect methods involved measuring the rate of disappearance of NADPH. We assessed the precision and reproducibility of each method. One of the indirect assays proved to be far superior to the other methods. Results of each of the methods were correlated with one another. We present the normal reference intervals for glutathione peroxidase activity for all four methods.