Digestive Diseases: Hydrogen Breath Test

The hydrogen breath test is used to diagnose lactose intolerance or determine if abnormal bacteria is present in the colon.

What Is Lactose Intolerance?

Lactose intolerance is the inability to digest lactose, the sugar found in milk. It causes cramping, bloating, gas, or diarrhea any time dairy products are consumed. Lactose intolerance occurs due to the body's lack of lactase, an enzyme normally produced by the small intestine that is needed to digest lactose.

What Happens During the Test?

During the test, which at the Cleveland Clinic lasts about 2 hours, you will be asked to drink a lactose-containing beverage. The beverage may cause cramping, bloating, gas, or diarrhea.

Fifteen minutes after drinking the beverage, you will be instructed to blow up balloon-like bags every 15 minutes for two hours.

The air you breathe into these bags is tested frequently for the presence of hydrogen. Normally, very little is detected in breath. However, hydrogen and other gases are produced when undigested lactose in the colon is fermented by bacteria.

Raised hydrogen breath levels indicate the improper digestion of lactose, which could lead to a diagnosis of lactose intolerance or the presence of abnormal bacteria in the colon.

How Do I Prepare for the Test?

Tell your doctor if:

• You have just had a colonoscopy. If so, you will need to wait a few weeks after the colonoscopy before this test can be performed.
• You are pregnant, have a lung or heart condition, have any diseases, or if you are allergic to any medications.

Other Guidelines

• Do not eat or drink anything (including water) for at least 8 hours before the procedure. If you need to take medicine, take them only with a small sip of water 8 hours before the procedure.
• Do not take any antibiotics for 2-4 weeks before the test. Take only the medications approved by your doctor before the procedure. Do not discontinue any medication without first consulting with your primary or referring doctor.
• Do not chew gum on the day of the test.

Your doctor may have other recommendations in addition to, or instead of, the ones listed above. Ask your doctor to provide you with written instructions prior to your test.

What Happens After the Test?

You may resume your normal activities and diet. A health care provider will discuss the results of the test with you.

Reviewed by The Cleveland Clinic Department of Gastroenterology.