Lactose Tolerance Tests

Lactose tolerance tests measure your body's ability to break down lactose. Lactose is a type of sugar found in milk, cheese, ice cream, and other dairy products. Normally, an enzyme (a protein that speeds up certain chemical reactions in your body) called lactase breaks down lactose into simpler sugars.

These sugars are absorbed by your body and turned into energy. If your body doesn't make enough lactase, you won't be able to properly digest foods that contain lactose. When you can't digest all of the lactose you eat or drink and it passes into your colon, it's called lactose malabsorption.; Lactose malabsorption can cause uncomfortable symptoms such as gas, bloating, and diarrhea within 30 minutes to 2 hours after drinking milk or eating other dairy products.; Getting the symptoms of lactose malabsorption after you eat or drink products with lactose is called lactose intolerance.; There are two types of lactose tolerance tests: Hydrogen breath test.

This test measures the amount of hydrogen gas in your breath before and after you drink a liquid containing lactose. If you can't digest all the lactose, it gets broken down by bacteria in your large intestine. This creates extra hydrogen gas, which you breathe out.

This is the most common way to test for lactose intolerance.; Glucose blood test. This test involves a series of blood tests that measure the level of glucose (a type of sugar) in your blood before and after you drink a liquid containing lactose. If you are lactose intolerant, you usually won't have an increase in blood glucose.;

Why this test is done

You may need this test if you have symptoms of lactose intolerance. Symptoms usually happen within 30 minutes to 2 hours of eating or drinking dairy products. They can include:

• Diarrhea
• Abdominal (belly) pain
• Bloating
• Gas
• Nausea

How to prepare

To prepare for either type of test, you will need to:

• Fast (not eat or drink) for eight to 12 hours before the test
• Stop taking antibiotics for two to four weeks before the test
• Not smoke or exercise strenuously the day before the test

You may also need to stop taking certain medicines before this test, such as laxatives, antacids, and stool softeners, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

If you are having a breath test, you may need to brush your teeth or rinse your mouth shortly before the test.

Sample type

Blood

Other names for this test

hydrogen breath test, oral lactose tolerance, lactose tolerance serum test, lactose intolerance test, lactose breath test, disaccharide absorption test