How to test for lactose intolerance

Lactose intolerance is a common ailment that involves the inability to break down and digest lactose, a type of sugar typically found in milk and other dairy products. There are several ways to test for the condition.

Yes, there are several methods of testing for lactose intolerance.  These tests may be performed partly at home or in a clinical setting.

The most common lactose intolerance test is called the hydrogen breath test. This test will be ordered by your healthcare provider. Your provider will likely review the preparation and test instructions with you prior to the procedure. This usually involves: 

• Avoiding certain medications, like laxatives and antibiotics, prior to testing
• Fasting and avoiding heavy exercise before the test
• Breathing into a special balloon or collection tube for a baseline sample
• Drinking the test liquid, which contains a premeasured amount of lactose
• Taking breath samples at set times specified by the test, typically every 30 minutes over several hours

The hydrogen breath test measures how much hydrogen gas is in your breath. Normally, very little hydrogen gas is found in the air we exhale, but if your body has difficulty breaking down lactose, those levels will rise. Test results showing an abnormally high level of hydrogen gas in your breath samples may suggest that you may have lactose intolerance.

The stool acidity test can be used to look for lactose intolerance in infants and small children. This test is typically performed by a pediatrician or a specialist. The test analyzes the stool to see if it contains higher than expected levels of glucose, lactic acid and other fatty acids. Elevated amounts of these substances may indicate lactose intolerance.

Another way to test for lactose intolerance is through a series of blood tests that measure changes in your blood sugar after you consume a liquid that contains lactose. When lactose is broken down and absorbed by the intestines, blood sugar levels normally rise over the next two hours. If this doesn't happen, it may indicate lactose intolerance.

If you suspect you have lactose intolerance, speak with your healthcare provider about your concerns. They can help determine if a lactose intolerance test is appropriate for you. For people who have this condition, an over-the-counter lactose intolerance supplement may be recommended.

Updated by Julie McDaniel, MSN, RN, CRNI, August 2024.