Hydrogen Breath Test

Also known as: breath test, small intestinal bacterial overgrowth hydrogen breath test.

What is a hydrogen breath test?

If a doctor suspects that a patient is experiencing digestive problems where food is not being digested properly, he or she may order a hydrogen breath test.

Hydrogen is produced by bacteria in the digestive tract. If a large amount of hydrogen is detected by the hydrogen breath test, it’s an indication that a large amount of unabsorbed food has reached the intestines.

What happens during the procedure?

After fasting for 12 hours, a patient fills a balloon using their breath. Then the patient consumes a test sugar such as lactose and glucose or lactulose which is a non-absorbable sugar, and repeats the test every 15 minutes for several hours.

Is any special preparation needed?

The patient needs to avoid eating for 12 hours before the hydrogen breath test.

What are the risk factors?

There are no risks related to the hydrogen breath test.

Reviewed by: Carrie Firestone Baum, MD

This page was last updated on: September 16, 2025 12:41 PM