Is there any difference in sensitivity or specificity when Helicobacter pylori is detected in the stool vs. the blood?
—FELIX N. CHIEN, DO, Newport Beach, Calif.

Many noninvasive tests diagnose H. pylori, including serology, polymerase chain reaction, stool antigen testing, and the urea breath test (UBT). The best choice for each patient is determined by the indication for the test, cost, convenience, and problems with sensitivity and specificity. The most cost-effective initial tests are the serologic tests and the fecal antigen tests. Serology is inexpensive and can be done with office-based kits using whole blood at $10 (sensitivity and specificity 80%) or in laboratories at a higher cost ($40-$75) with a sensitivity of 90%. The stool antigen assay, which has a sensitivity of 94% and specificity of 86%, can be useful for primary diagnosis of H. pylori as well as for eradication. Recommended by the American College of Gastroenterology as the best nonendoscopic test for documenting H. pylori, the UBT is very sensitive (88%-95%) and specific (95%-100%), but it is costly ($60-$100). Moreover, since the fecal antigen assay and UBT use urea as a marker for H. pylori, there can be false negatives in patients taking proton pump inhibitors (PPIs), antibiotics, or bismuth, leading to the recommendation that PPIs be discontinued for 7-14 days prior to testing.
—Susan Kashaf, MD, MPH