Which noninvasive test detects Helicobacter pylori infection by measuring exhaled carbon dioxide after ingestion of labeled urea?

• A. Serology
• B. Stool antigen test
• C. Endoscopy
• D. Urea breath test

Answer: (D)

The method hinges on the urease activity of Helicobacter pylori to reveal active infection noninvasively. After you swallow urea labeled with a carbon isotope, H. pylori in the stomach breaks it down into ammonia and carbon dioxide. The labeled CO2 is absorbed into the bloodstream and then exhaled in the breath. Measuring the amount of labeled CO2 in the breath tells you whether urease—and thus live bacteria—are present in the stomach. This test is also useful to confirm eradication after treatment because it directly reflects current infection.

Other options have different limitations. Serology looks for antibodies and can’t reliably distinguish past from current infection. Stool antigen tests detect bacterial components indicating current infection but require handling stool. Endoscopy is invasive and involves direct visualization with biopsy.