BackgroundMetabolic syndrome (MetS) is a complex metabolic disease connected especially with lipid and carbohydrate disturbances. It is postulated that oxidative stress (OS) is linked to metabolic syndrome, constituting a novel component of its pathogenesis.AimWe aimed to examine the plasma level of oxidatively modified proteins––advanced oxidation protein products (AOPP) and ischemia modified albumin (IMA)––as well as thiol (SH) groups and evaluate their connection with metabolic agents in relation to MetS prevalence.Subjects and methodsThe levels of AOPP, IMA and SH groups were measured spectrophotometrically in 106 patients with MetS risk factors and in 32 control subjects.ResultsThe levels of examined parameters differed significantly between patients with MetS risk factors and the control group. AOPP significantly correlated with glucose (r = 0.30, p = 0.008), HDL-Ch (r = −0.34, p = 0.005), TG (r = 0.48, p < 0.001) and fibrinogen (r = 0.37, p < 0.001). The levels of AOPP and IMA increased progressively with the number of MetS risk factors, being the most significant for AOPP. The highest values of AOPP were associated with the presence of at least three risk factors. Only AOPP were an independent determinant for MetS occurrence in the studied population (OR = 2.72, p = 0.04). Mutual dependence between metabolic, oxidative stress and inflammatory parameters was revealed.ConclusionsOxidative modifications of proteins are increased in MetS and accumulation of MetS risk factors enhances manifestation of OS. AOPP is the most appropriate parameter for determination of OS, with potential diagnostic value in MetS patients.