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Lactose Tolerance Hydrogen (Breath)

Does this test have other names?

Hydrogen breath test, HBT, lactose breath test

What is this test?

This test measures the amount of hydrogen gas in your breath at regular intervals. It will show how well your body breaks down lactose, the sugar found in dairy products, and fructose, the sugar in fruit. This test also shows whether you have a high amount of bacteria in your small intestine.

Normally, the lactose you eat is broken down in your small intestine. If it can't be broken down there, it goes to your colon, or large intestine. In the colon, the lactose can ferment, causing excess hydrogen.  This extra hydrogen is absorbed into your blood and travels to the lungs, where you release it in your breath. 

Why do I need this test?

You might have this test if you have symptoms of lactose intolerance. Symptoms include:

  • Gas

  • Stomach cramps

  • Bloating

  • Diarrhea, especially after you eat or drink milk and other dairy products such as ice cream and cheese

More than half of people of certain ethnic backgrounds have lactose intolerance.

You also might have this test if you have an intestinal problem like inflammatory bowel disease or a malabsorption syndrome like short gut syndrome. Infants who are not gaining enough weight may also have this test. 

What other tests might I have along with this test?

Your doctor might also order a glucose tolerance test, which is used mainly to diagnose diabetes. A glucose tolerance test can help tell whether your symptoms are caused by lactose intolerance or diarrhea from malabsorption.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Normal test results compare your exhaled breath before and after you drink liquid containing sugar. The amount of hydrogen gas in your breath should increase by no more than 50 parts per million.

If your breath test shows you are exhaling large amounts of hydrogen, it may mean you aren't fully digesting and absorbing lactose. 

How is this test done?

This test requires several breath samples over a period of time. You will first breathe into a bag. Then you will drink a beverage that contains lactose, fructose, or other sugars. You must drink it all. Every 15 minutes for the next two to four hours, you will be asked to breathe into a bag. Each time, a technician will empty the bag with a syringe.

Does this test pose any risks?

If you are lactose intolerant, drinking the sugar may cause bloating, cramps, diarrhea, and gas. 

What might affect my test results?

Your results could be affected if you:

  • Exercise strenuously before or during testing 

  • Take antibiotics within a month before testing

  • Eat or drink while testing

  • Smoke before or during testing

  • Chew gum or breath mints during testing 

How do I get ready for this test?

  • Stop taking antibiotics at least four weeks before your test.

  • The day before your test, do not eat high-fiber foods such as beans or whole-grain cereals. Don't drink carbonated beverages.

  • Fast for 12 hours before testing. That means you should have nothing to eat or drink.

  • Don't smoke the day before testing.

  • Don't exercise strenuously the day before testing.

  • Brush your teeth two hours before your test begins.

Your provider may give you additional dietary instructions. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.