Background and aims Advanced oxidation protein products (AOPP) represent an exquisite marker of oxidative stress, their role in the pathophysiology of chronic renal failure might be of great importance. The aim of the study was to determine serum and urinary levels of AOPP in children with nephrotic syndrome (NS).

Methods The study included 40 children, aged 12 to 18 years, of whom 25 were diagnosed with acute NS, 8 children with chronic NS and 7 children with chronic kidney disease (CKD) stage 3–5. The control group consisted of 20 healthy children. Assessment of the serum and urinary excretion of AOPP was based on spectrophotometric detection method (Kalousova M. et al., 2002).

Results Serum AOPP level in children with acute NS constituted 24,40 ± 4,27 mM/l compared to controls (36,91 ± 3,86 mM/l), however urinary excretion of AOPP was significantly higher (31,1 ± 4,6 mM/l vs. 12,14 ± 2,7 mM/l in controls; p < 0,05). In the group of children with chronic NS serum and urinary levels were higher but not significantly as compared to controls (54,70 ± 7,6 mM/l and 22,46 ± 3,2 mM/l, accordingly; p > 0,05). A remarkable increase of the serum excretion of AOPP in CKD stage 3–5 was noted (130,5 ± 22,83 mM/l; p < 0,05).

Conclusions The determination of AOPP in serum and urine is a reliable marker to estimate the degree of oxidant mediated protein damage in patients with nephrotic syndrome and to assess the progression of chronic kidney disease.