At advanced gastric int. metaplasia or at dysplasia, is the urea breath test still effective?

Yes: The breath test for helicobacter pylori contains a chemical called urea, which is attached to a carbon atom. The bacteria break down the urea thereby releasing the carbon, which is eventually exhaled in the breath. The presence of the bacteria is highly associated with malignant transformation in the stomach and the presence of dysplasia is a suggestion that cancer is forming and must be treated