Urea (13C)

How it works

If H. pylori is present, its urease enzyme hydrolyses the ingested labelled urea into ammonia and labelled carbon dioxide, which is absorbed and exhaled and then measured in breath samples.

Prescribing in practice

• The test can give false-negative results if the patient has recently taken proton pump inhibitors, antibiotics or bismuth, so these should be stopped for the recommended washout period beforehand.
• It is taken after fasting, usually with a citric acid drink to delay gastric emptying and improve test performance.
• It is a purely diagnostic, non-radioactive agent suitable for confirming eradication after treatment as well as initial diagnosis.

Monitoring

No drug monitoring is required; the test outcome is determined by comparing labelled carbon dioxide in pre- and post-dose breath samples.

Counselling the patient

• Avoid eating before the test and follow the fasting instructions you are given.
• Tell the team if you have recently taken acid-suppressing medicines or antibiotics, as these can affect the result.

Evidence & guidelines

The carbon-13 urea breath test is endorsed by NICE as a non-invasive method for diagnosing H. pylori and confirming eradication.