Definition of Lactose tolerance tests:

Lactose tolerance tests measure the ability of your intestines to break down lactose, a type of sugar found in milk and other dairy products.

See also: Lactose intolerance

How the test is performed:

Two common methods include:

• Lactose tolerance blood test
• Hydrogen breath test

The hydrogen breath test is the preferred, noninvasive method. It measures the amount of hydrogen in the air you breathe out. You will be asked to breathe into a balloon-type container. Then, you will be asked to drink a flavored liquid containing lactose. Samples of your breath are collected at predetermined time periods and the hydrogen level is checked. Normally, very little hydrogen is detected in your breath. But if your body has trouble breaking down and absorbing lactose, hydrogen levels increase.

The lactose tolerance blood test looks for the presence of glucose in your blood. Your body creates glucose when lactose breaks down. The test requires several blood samples taken before and after you drink the lactose solution described above. For information on how a blood sample is obtained, see venipuncture.

How to prepare for the test:

You should not eat for 8 hours before the test. Avoid strenuous exercise for 8 hours before the test.

How the test will feel:

There should not be any pain or discomfort when giving a breath sample.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

Your doctor may order these tests if you have signs of lactose intolerance.