Background/Aims: Oxidative stress has been considered a nontraditional risk factor for cardiovascular disease in the chronic kidney disease (CKD) population, possibly triggered by uremic toxicity. Methods: A chromatographic method with coulometric detection was adapted to directly and simultaneously determine cysteine (Cys) and cystine (Cyss) in plasma samples. Healthy subjects and CKD subjects in different stages were analyzed. The free Cys and free Cyss levels in their plasma were determined, and the reduction potential [E_h(Cyss/2Cys)] was calculated with the Nernst equation. Results: Healthy plasma presented E_h(Cyss/2Cys) of –123 ± 7 mV. Plasma E_h(Cyss/2Cys) correlated significantly with creatinine levels (p < 0.0001, r = 0.62). Conclusion: Plasma E_h(Cyss/2Cys) correlated with increased levels of plasma creatinine, supporting the view that uremia triggers oxidative stress. In addition, it may be used as a quantitative oxidative stress biomarker in uremic conditions.

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