The invention relates to diagnostic methods for assessing the need of a subject for treatment with an anti-oxidant, or alternatively, for determining the utilization efficiency and ultimate effectiveness of anti-oxidant therapy in subjects having been treated with antioxidants. More specifically, the methods of the present invention are particularly useful in prophylactic assessment of individuals at risk for developing diseases or conditions in which oxidative stress plays a role, such that an appropriate therapeutic regimen can be prescribed for that individual, thus leading to alternative therapies and/or life style changes. The invention further relates to methods for assessing the need for, the utilization efficiency and the effectiveness of therapy in subjects having received therapy with specific antioxidant and immune enhancing formulations. Kits are also provided for measuring the levels of markers of oxidative stress and immune cell numbers.