Analytical and Clinical Validation of Rapid Chemiluminescence Enzyme Immunoassay for Urinary Thioredoxin, an Oxidative Stress-Dependent Early Biomarker of Acute Kidney Injury.

Background: Oxidative stress is now recognized to be an important therapeutic target in kidney diseases. However, there are currently no biomarkers that can be used clinically to diagnose renal oxidative stress. Methods: A rapid assay system for urinary thioredoxin 1, an oxidative stress-dependent biomarker of acute kidney injury (AKI), was developed as a chemiluminescence enzyme immunoassay and validated analytically and clinically. Results: Analytic evaluation revealed that hemolytic hemoglobin caused measurements to be abnormally high, above the detectable range. However, urine sediment containing red blood cells did not affect the measurements. Assays using our proposed chemiluminescence enzyme immunoassay were completed within as little as 6 min, whereas a conventional ELISA > 4 h. Aciduria < pH 6.0 led to a significant underestimation of thioredoxin 1 concentrations. However, the effects of aciduria were completely reversible with use of a buffer developed for pH adjustment. Urinary thioredoxin 1 was increased in patients with AKI, but was unaffected by extrarenal oxidative stress diseases, including hypoxemia and myocardial infarction, or by chronic kidney disease in which serum creatinine concentrations were comparable. Conclusions: These results suggest that the chemiluminescent enzyme immunoassay system for urinary thioredoxin 1 enables rapid and specific diagnosis of AKI associated with oxidative stress.