REPLY to “Association Between Plasmatic Oxidative Stress and Thrombosis in Primary Antiphospholipid Syndrome”

We read with great interest the article by Vaz et al. who investigated markers of oxidative stress in 70 thrombotic primary antiphospholipid patients (PAPS) and in 74 controls [1]: the authors were surprised not to fnd elevated plasma levels of such markers, amongst which 8-isoprostanes, in their PAPS population; this seem contrary to what was found in a recent meta-analysis, where pooled data from PAPS patients showed higher urinary/plasma concentrations of 8-isoprostanes compared to systemic lupus erythematosus with APS and to systemic lupus without APS [2]. There are potential explanations for the discrepancy noted by Vaz et al. in terms of methodology of 8-isoprostane measurement, patient population, comorbidities, treatment and expression of antiphospholipid antibody results. With regards to the frst issue, plain immunoassays for 8-isoprostane, not preceded by a purifcation step, are poorly reliable in plasma and less so in urine owing to the cross-reactivity between several prostaglandins and to the binding of the antibody that may be hampered by impurities, therefore underestimating true values [3]. In addition, total antioxidant capacity is a non-specifc method to assess oxidative imbalance; a more specifc assay evaluating specifc antioxidant pathways, such as the blood hydrogen peroxide break-down activity may provide more precise and reliable results.