The urea breath test may be falsely negative in patients who have taken antibiotics within the past 4 weeks, bismuth compounds within the past 4 weeks, or anti-secretory agents such as PPIs within the past 2 weeks.  This is also true for the fecal antigen test.  Confirming eradication of H. pylori is only indicated in a few circumstances.   However, if confirmation of eradication is done and either the urea breath or fecal antigen tests are used, then the appropriate amount of time needs to have passed after the completion of eradication therapy before the confirmation test is performed.