Lactose Tolerance Tests

Why this test may be ordered

• Diagnose lactose intolerance
• Check for other health conditions that may cause similar symptoms, such as irritable bowel syndrome, celiac disease, small intestinal bacterial overgrowth (SIBO), Crohn's disease, or ulcerative colitis

Preparation and collection

To prepare for either type of test, you will need to: Fast (not eat or drink) for eight to 12 hours before the test, Stop taking antibiotics for two to four weeks before the test, Not smoke or exercise strenuously the day before the test. You may also need to stop taking certain medicines before this test, such as laxatives, antacids, and stool softeners, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

Your health care provider may order a hydrogen breath test or a glucose blood test. You will drink a flavored liquid that contains lactose. You will breathe into the container again 30 minutes later and every 30 minutes for a few hours. More blood samples will be taken at specific intervals, usually at 30 minutes, one hour, and two hours.

If you are lactose intolerant, you may feel cramps or bloating after drinking the lactose beverage. There are no other risks to having a hydrogen breath test. There is very little risk to having a blood test.

Understanding results

Getting the symptoms of lactose malabsorption after you eat or drink products with lactose is called lactose intolerance.

• Hydrogen breath test: increased hydrogen: An increased level of hydrogen and worsening symptoms after drinking lactose. This probably means you have lactose intolerance. Limitation: Lactose intolerance is not the same as an allergy to milk or dairy. Next step: If you are diagnosed with lactose intolerance, you should be able to manage your condition by limiting or avoiding foods with lactose, such as milk and cheese.
• Hydrogen breath test: little or no increase in hydrogen: Little or no increase in hydrogen after drinking lactose. This means your symptoms are probably not caused by lactose intolerance. Limitation: But sometimes you can have a negative result and still have lactose intolerance. Next step: You may need more tests to figure out the cause of your symptoms.
• Glucose blood test: glucose did not increase: Your glucose levels did not increase after drinking lactose. This probably means you have lactose intolerance. Limitation: Lactose intolerance is not the same as an allergy to milk or dairy. Next step: If you are diagnosed with lactose intolerance, you should be able to manage your condition by limiting or avoiding foods with lactose, such as milk and cheese.
• Glucose blood test: glucose increased: Your glucose levels increased. This means your symptoms are probably not caused by lactose intolerance. Limitation: But if you have diabetes, your blood glucose may increase even if you have lactose intolerance. Next step: You may need more tests to figure out the cause of your symptoms.

• If you are lactose intolerant, you may feel cramps or bloating after drinking the lactose beverage. The supplied source states there are no other risks to having a hydrogen breath test. There is very little risk to having a blood test; there may be slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
• A negative result does not completely rule out lactose intolerance; further testing may be needed.

What to do next

Be sure to talk to your provider about planning your diet and/or taking lactase supplements.

• Diarrhea
• Abdominal (belly) pain
• Bloating
• Gas
• Nausea

Evidence source

Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.

U.S. National Library of Medicine: Lactose Tolerance Tests

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