Aim: The aim of this study was to extensively evaluate four fully-automated photometric methods directly measuring antioxidant capacity; ferric ion reducing power, total antioxidant status, total antioxidant response, total thiol and to reveal the weak and strong sides of the assays.

Material and methods: Blood samples were obtained from 125 healthy subjects. Serum samples and several endogenous and exogenous antioxidant molecules were used for analytical determinations. The performance characteristics of the methods were compared and the relationships between these methods results were investigated.

Results: According to the data obtained from this study, the ferric ion reducing power method was inadequate for measuring thiol compounds, carotenoid and uric acid. Repeatability scores for the total antioxidant response method were lower than the other three methods, and the total antioxidant response method was found to be weak to measure uric acid. However, total antioxidant response method had a higher linearity than the other methods. The total antioxidant status method was the least affected by hemolysis and lipemia interference. Total thiol methodwith the lowest limit of detection, high sensitivity, and repeatabilitywas found to be efficient.

Conclusion: Though there is currently no standard method used to determine the antioxidant activity of a compound, the use of different methods and assessing the results gathered from the different methods is a convenient way to evaluate antioxidant capacity.