How is lactose intolerance diagnosed?

The most common test for the diagnosis of lactase deficiency is the hydrogen breath test. This test is done at an outpatient clinic or doctor's office. In practice, many doctors will ask patients who suspect they have lactose intolerance to avoid milk and dairy products for 1 or 2 weeks to see if their symptoms subside, and will then confirm the diagnosis with the hydrogen breath test. The hydrogen breath test measures the amount of hydrogen in the breath after drinking a lactose-loaded beverage.

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