Urine test strip ascorbic acid (vitamin C) has been associated with false-negative reagent strip reactions for blood. Both Multitistix and Chemstrip have modified their reagent strips to reduce this interference to very high levels of ascorbic acid, and Chemstip overlays the reagent pad with an iodate-impregnated mesh that oxidizes the ascorbic acid prior to its reaching the reaction pad. False-negative reactions can result when urine with a high specific gravity contains crenated red blood cells that do not lyse when they come in contact with the reagent pad. Decreased reactivity may also be seen when formalin is used as a preservative or when
Vitamin C efficiency decreases as amounts increase. Intravenous administration bypasses this. Doing so makes it possible to achieve plasma concentrations of 5 to 10 millimoles/liter (mmol/L), which far exceed the approximately 0.2 mmol/L limit from oral consumption. The theories of mechanism are contradictory. At high tissue concentrations ascorbic acid is described as acting as a pro-oxidant, generating hydrogen peroxide (HO) to kill tumor cells. The same literature claims that ascorbic acid acts as an antioxidant, thereby reducing the adverse effects of chemotherapy and radiation therapy. Research continues in this field, but a 2014 review concluded: "Currently, the use of high-dose intravenous vitamin