Serum Advanced Oxidation Protein Products as Biomarkers of Oxidative Stress in Patients With Chronic Kidney Disease

Background: Chronic kidney disease (CKD) is characterized by progressive deterioration of renal function and is associated with increased oxidative stress, which contributes to inflammation, fibrosis, and cardiovascular complications. Advanced Oxidation Protein Products (AOPPs) are reliable biomarkers of oxidative protein damage and have emerged as potential indicators of CKD progression. This study aimed to evaluate serum AOPP levels and determine their association with CKD severity. Methods: An analytical cross-sectional study was conducted among 120 patients with CKD stages 2–5 and 30 age- and sex-matched healthy controls at a tertiary care hospital. Serum AOPP concentrations were measured using enzyme-linked immunosorbent assay (ELISA). Routine biochemical parameters, including serum creatinine, estimated glomerular filtration rate (eGFR), serum albumin, and phosphate, were analyzed using standard laboratory methods. CKD severity was classified according to KDIGO guidelines. Statistical analyses included independent sample t-test, one-way ANOVA, Pearson's correlation, and multiple linear regression. Results: CKD patients exhibited significantly higher serum AOPP levels than healthy controls (138.6 ± 39.8 vs. 56.3 ± 12.4 µmol/L, p<0.001). AOPP concentrations increased progressively across CKD stages, from 92.8 ± 18.6 µmol/L in stage 2 to 185.1 ± 30.2 µmol/L in stage 5 (p<0.001). Serum AOPPs demonstrated a strong positive correlation with serum creatinine (r=0.694, p<0.001) and serum phosphate (r=0.516, p<0.001), while showing a significant negative correlation with eGFR (r=−0.731, p<0.001) and serum albumin (r=−0.408, p<0.001). Multiple regression analysis identified serum creatinine and eGFR as independent predictors of circulating AOPP levels. Conclusion: Serum AOPP concentrations increase significantly with worsening CKD severity and are closely associated with declining renal function. AOPPs may serve as a valuable biomarker for assessing oxidative stress and monitoring disease progression in patients with chronic kidney disease.