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How is lactose intolerance diagnosed?

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Many people think that they or their children are lactose intolerant without being tested or diagnosed.1 As a result, many people avoid or greatly limit their intake of dairy products,2 which are rich in calcium and vitamin D. These nutrients help to build strong bones. Most people who are lactose intolerant are able to consume some amount of lactose without symptoms.

It's not always easy to tell based on symptoms alone whether a person has lactose intolerance or another condition.2 Many common health problems have similar symptoms. For instance, lactose intolerance has many of the same symptoms as irritable bowel syndrome (IBS); however, IBS can also cause constipation.

If lactose intolerance is suspected, the person may be asked to stop eating or drinking foods that contain lactose for a brief time. If the symptoms go away, then this information may be all a health care provider needs for a diagnosis.2 The following tests also can help diagnose lactose intolerance:

  • Hydrogen breath test. For this test, a person drinks a beverage that has lactose in it. Then, the hydrogen level in the breath is measured at set time intervals. Hydrogen gas is formed when lactose is not digested, so high breath hydrogen is a likely sign of problems digesting lactose.1
  • Lactose intolerance test. For this test, blood samples are taken before and after a person drinks a beverage that contains lactose. The amount of sugar (glucose) in the blood is measured. Levels that do not change can suggest problems digesting lactose.1 The hydrogen breath test is preferred over this test.3
  • Stool acidity test. This test is used for infants and young children. The stool is checked for certain acids that form when lactose is not digested. Glucose in the stool also suggests problems digesting lactose.

  1. Suchy, F. J., Brannon, P. M., Carpenter, T. O., Fernandez, J. R., Gilsanz, V., Gould, J. B., et al. (2010). NIH consensus development conference statement: Lactose intolerance and health. NIH Consensus and State-of-the-Science Statements, 27(2), 1–27. PMID 20186234 [top]
  2. American Gastroenterological Association. (2010). Understanding food allergies and intolerances. Retrieved April 24, 2012, from External Web Site Policy [top]
  3. MedlinePlus Encyclopedia. (2010). Lactose intolerance tests. Retrieved May 29, 2012, from [top]

Last Reviewed: 05/06/2014
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