I would suggest you to use a more appropriate and robust method, such as TAC-IT kit for detecting total antioxidant capacity in whole blood, that is sold by an Italian Company (www.solosal.it)
I agree with comments above. This is indeed an often ignored (yet very important) consequence of membrane lipid peroxidation. The polar modifications to membrane lipids makes them permeable to ions. A quick Goggle search turned up https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2098729/ .