Urea breath tests detect current H. pylori infection. This test is based on production by H. pylori of powerful urease, an enzyme that converts urea to ammonium and carbon dioxide (CO2) (Bazzoli et al., 1997; Vakil and Vaira, 2004). When infected with H. pylori, high urease activity is present in the stomach. A dose of urea labeled with either 13C or 14C is taken by the subject. The urease-catalyzed reaction then takes place in the mucus layer. The labeled CO2 diffuses to the epithelial cells and then is carried in the bloodstream and ultimately is released in the exhale. The labeled CO2 in the subject's breath can be measured. The amount of the labeled CO2 is related to the urease activity, which indicates the presence or absence of H. pylori infection (Bazzoli et al., 1997; Logan, 1993; Vakil and Vaira, 2004). The amounts of the isotopic CO2 can be measured by various techniques, and the results are expressed relative to the endogenous CO2 production. The sensitivity and specificity of breath tests range from 95% to 97%, although this method has been reported to be less reliable for patients with gastric surgery or in patients who take proton pump inhibitors or ranitidine (Vakil and Vaira, 2004). In a study involving 20 volunteers, Cutler et al. found that ranitidine at standard dose (150 mg b.i.d.) or high dose (300 b.i.d.) does not decline breath test results reproducibly, and ranitidine does not need to be discontinued before a urea breath test (Cutler etal., 1998).
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