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. Undigested lactose in the colon is fermented by bacteria and produces hydrogen and other gases. Hydrogen is absorbed, carried by the blood to the lungs, and exhaled. Raised levels of hydrogen in the breath within 90 minutes indicate improper digestion of lactose. This test has a 90% sensitivity to determine lactose intolerance. Certain foods, medications, and cigarettes can affect the test result, so the patient will be instructed to avoid these prior to taking the test.

Foods high in lactose

The most common high-lactose foods include:

  • Milk, milkshakes and other milk-based beverages
  • Whipping cream and coffee creamer
  • Ice cream, ice milk, sherbet
  • Cheese
  • Butter
  • Puddings, custards
  • Cream soups, cream sauces
  • Foods made with milk

Other foods that MAY contain lactose in smaller quantities include:

  • Bread and baked goods
  • Milk chocolate
  • Salad dressings and sauces
  • Breakfast cereals and cereal bars
  • Instant potatoes, soups, rice and noodle mixes
  • Lunchmeats
  • Candies and other snacks
  • Mixes for pancakes, biscuits, and cookies
  • Margarine
  • Organ meats (such as liver)
  • Sugar beets, peas, lima beans

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