Decreased total antioxidant capacity but normal lipid hydroperoxide concentrations in sera of critically ill patients.

Oxidative stress (when free radical generation exceeds antioxidant defense) occurs in many human diseases and makes significant contributions to their pathogenesis. We automated assays estimating the antioxidant status of serum, and lipid hydroperoxide concentrations using the Monarch analyzer. In this assay, the antioxidant status of serum is measured by its ability to inhibit generation of free radicals from 2,2'-amino-di-[3-ethylbenzthiazole sulphonate] by metmyoglobin and hydrogen peroxide. The assay for measuring lipid peroxidation products in serum utilizes the ability of lipid hydroperoxides to generate methylene blue from 10N-methylcarbamyl 3,7-dimethylamino 10H-phenothiazine. We detected no lipid hydroperoxide in sera obtained from 24 controls. The mean antioxidant status was 1.69 mmol/l (SD; 0.20 mmol/l) in controls. The antioxidant capacity of serum was significantly reduced in sera of critically ill patients in the medical intensive care unit (mean = 1.05, SD = 0.26 mmol/l) with p value less than 0.05 by independent t-test, two tailed. Lipid peroxidation products were not significantly elevated in critically ill patients, however lipid peroxidation products were significantly elevated in hemodialysis patients (mean = 1.40, SD = 0.47 mumol/l) and in some kidney transplant recipients. We conclude that antioxidant capacity of sera in critically ill patients is significantly reduced.