Hydrogen Breath Test and Lactose Intolerance

Medically Reviewed by Minesh Khatri, MD on September 18, 2023
2 min read

The hydrogen breath test is a method used to diagnose 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.

During the hydrogen breath test, which takes 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 the 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.

Before the hydrogen breath 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
  • Do not eat or drink anything (including water) for at least 12 hours before the hydrogen breath test. If you need to take medicine, take only with a small sip of water 12 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.

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