Helicobacter pylori tests (breath and stool)

The breath and stool tests for Helicobacter pylori look for this bacterium without putting any instrument inside the body, which is why they're called noninvasive. All it takes is breathing out or providing a stool sample, in other words, a sample of poop. The tests show whether there's an infection and, after treatment, whether the infection has been cured.

The breath test relies on a tool that belongs to the bacterium itself. The person swallows urea (a waste product normally found in the blood) made with labeled carbon: carbon the lab can tell apart from ordinary carbon, like a marked bill whose serial number has been written down. H. pylori has urease, an enzyme, meaning a protein that does one specific chemical job, in this case splitting urea. Our own cells don't have urease. Urease breaks urea down into ammonia and carbon dioxide, and that carbon dioxide passes into the blood and leaves the body in the air you breathe out. Finding the labeled carbon in the breath is like the marked bill turning up at the other end: it shows the urea went through urease.

The stool test looks for a different clue: antigens, which are proteins that come from H. pylori. It's like knowing someone was in a room because of the things they left behind. There's no need to see the bacterium itself; finding those proteins that belong to it in the sample is enough.