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Lactose Intolerance - Exams and Tests

If your doctor thinks you have lactose intolerance, he or she will ask questions about your medical history and do a physical exam. Before making a diagnosis, your doctor may ask that you avoid dairy products for a short time to see if your symptoms improve. You may also be asked to bring in a sample of your stool. The stool of a person who has lactose intolerance is usually loose or watery. It also can be foamy.

To confirm a diagnosis, your doctor may order a:

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  • Hydrogen breath test. This is the most accurate lactose intolerance test. Before the test, you need to avoid certain foods and medicines and cigarettes. On the day of the test, you will drink a liquid that contains lactose and then breathe into a machine several times over a couple of hours. If the hydrogen levels in your breath are high, you may have lactose intolerance. This test is not usually done on babies and very young children, because it can cause severe diarrhea.
  • Lactose tolerance test. This test measures your blood sugar after you eat or drink lactose. After midnight on the night before the test, you should not eat or drink anything. On the day of your test, you will drink a liquid that contains lactose, which may cause gas or pain in your belly. Then your blood will be tested every 30 minutes for 2 hours. If your blood sugar levels do not rise, you may be lactose-intolerant. This test is not done on people who have diabetes. And it is usually not done on babies and very young children.

    This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http:// cancer .gov or call 1-800-4-CANCER.

    WebMD Medical Reference from Healthwise

    Last Updated: March 12, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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