How the Urea breath test works?

H. pylori that colonizes the gastric mucosa will produce an enzyme called Urease (catalyzes the breakdown of urea to produce ammonia + carbamate). 

The labeled Carbon-13 isotope urea breath test has become the gold standard to confirm eradication of H. pylori following appropriate treatment because serology will remain positive even after cure.

In this test, the patient drinks an urea solution (~100-200mL) containing a nonradioactive 13-Carbon isotope. Normally gastric urea is virtually all 12-Carbon isotope. If H. pylori Urease is present, the 13C-urea is hydrolyzed and the radiolabeled 13-Carbon dioxide is excreted from the lungs and can be detected in the patient’s expired breath around 30 minutes later. (Only detected if Urease breaks it down)

Samples are sent for mass spectrometry and elevated concentrations of 13-Carbon isotope is considered positive for H. pylori (96% sensitivity and 100% specificity) [3]. 

REFERENCES

1. Chapter 26: Stomach. Schwartz’s Principles of Surgery, 10e. Yuko Kitagawa; Daniel T. Dempsey
2. Mobley HLT. Urease. In: Mobley HLT, Mendz GL, Hazell SL, editors. Helicobacter pylori: Physiology and Genetics. Washington (DC): ASM Press; 2001. Chapter 16.
3. Berger A. Helicobacter pylori breath tests. BMJ : British Medical Journal. 2002;324(7348):1263.