XDH and chronic kidney disease: Herein, we aim to present the existing data regarding biomarkers of OS, pro-oxidants (oxidized albumin, advanced oxidation protein products, xanthine oxidase/dehydrogenase, nitrite/nitrate, malondialdehyde) and antioxidants (superoxide dismutase, catalase, vitamin E, total antioxidant capacity, N-acetylcysteine) that are most clinically relevant and have been more extensively studied in patients with chronic kidney disease, aiming to provide a clearer understanding of this complex area.