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
L-gulonolactone oxidase deficiency living in a malarial infested environment". He based his observation on evidence which indicates that G6PD deficient individuals display enhanced sensitivity to ascorbic acid induced hemolysis. Studies of human diseases have benefited from the availability of small laboratory animal models. However, the tissues of animal models with a GULO gene generally have high levels of ascorbic acid and so are often only slightly influenced by exogenous vitamin C. Guinea pigs, for instance, are a popular human model but lost the ability to synthesize L-gulono-gamma-lactone oxidase 20 million years ago. This is a major handicap for studies involving the endogenous