Oxidative stress, as assayed by a single test, cannot be used as a diagnostic tool.

The commonly used term "oxidative stress" (OS) is intuitively defined as an excess of pro-oxidative compounds, over antioxidants. The redox status is homeostatically controlled because on one hand, pro-oxidants are essential for normal body function, whereas, on the other hand, pro-oxidants (and OS) are associated with many diseases due to the risk of oxidative damage. One reason "to monitor the OS" is to identify people under OS and treat people under high OS by antioxidants, because it is believed that people under OS benefit from antioxidant supplementation more than others. This approach led to the production of many assay kits, based on the concentrations of different biomarkers in body fluids. Unfortunately, this expensive approach (evaluated at about a half a billion dollars per year) yields very limited results because: (i) the effect of antioxidants on the OS is not that simple and (ii) OS cannot be quantitated in terms of a universal criterion and the method-dependent OS yields different groups of people under OS. This conclusion gains strong support from analysis of the results of a previous study of the OS in more than 2000 participants, using many OS assays. The small overlapping between the "people under OS" as assayed by different biomarkers clearly shows that OS cannot be used as a diagnostic tool.