What is a hydrogen breath test?
A hydrogen breath test measures the amount of hydrogen in your breath after drinking a sugar solution. Certain digestive problems cause undigested sugar to be broken down by bacteria in the gut, which releases hydrogen gas that shows up in your breath.
Why is this test done?
- To check for lactose intolerance (difficulty digesting milk sugar)
- To check for fructose malabsorption
- To diagnose small intestinal bacterial overgrowth (SIBO)
- To investigate unexplained bloating, gas, or chronic diarrhea
How to prepare for the test
- Fast overnight (8 to 12 hours) before the test
- Avoid antibiotics and probiotics for several days beforehand, as instructed by Dr. Gattani
- Avoid smoking and strenuous exercise just before the test
What happens during the test
You will drink a sugar solution — the exact type (lactose, fructose, or glucose) depends on what your doctor is testing for. You will then breathe into a collection device every 15 to 30 minutes for about 2 to 3 hours, so hydrogen levels can be tracked over time.
What happens after the test
You can eat normally and go about your day right after the last breath sample. There is no recovery time needed.
Is this test safe?
Yes. It is non-invasive, uses no needles or radiation, and has no significant risks. Some people feel mild bloating during the test from the sugar solution, which passes on its own.
Frequently asked questions
No. It only involves drinking a solution and breathing into a device — there are no needles involved.
Fast overnight, and avoid antibiotics, probiotics, and smoking for the period your doctor advises before the test.
It is a well-established test for lactose intolerance, fructose malabsorption, and SIBO, though your doctor will interpret results alongside your symptoms and history.
Since the test tracks hydrogen levels over time, results are usually available on the same day.