To help diagnose lactose intolerance in individuals who have difficulties digesting dairy products, or sometimes as part of an investigation of malabsorption
Lactose Tolerance Tests
Lactose Tolerance Tests
Also Known As
Lactose Intolerance Test
Hydrogen Breath Test
Lactose Breath Test
Disaccharide Absorption Test
Oral Lactose Tolerance
This article was last reviewed
on
This article waslast modified
on March 25, 2021.
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At a Glance
Why Get Tested?
When To Get Tested?
When you have symptoms such as abdominal pain, bloating, gas, and diarrhea after consuming milk and other dairy products
Sample Required?
A series of breath samples exhaled into a collector, or a series of blood samples drawn from a vein in your arm
Test Preparation Needed?
Overnight fasting is required; nothing but water is permitted. Two weeks prior to the test, you must be off antibiotics and stomach medications, such as laxatives, antacids and stool softeners. Tell your healthcare practitioner about any other medications you are taking. Avoid strenuous activities. You may be instructed to brush your teeth and/or rinse your mouth with water prior to and during the breath test.
Accordion Title
Common Questions
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How is it used?
Lactose tolerance testing is used to help diagnose the cause of symptoms that suggest a reduced ability to digest lactose. These include abdominal pain and diarrhea following the ingestion of milk or dairy products. It may be ordered by itself or as part of a larger panel of tests when a secondary cause, such as malabsorption, is suspected. The hydrogen breath test is the more commonly ordered test. The blood test is not ordered as frequently.
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When is it ordered?
Testing is ordered when a person has signs and symptoms that suggest lactose intolerance that develop 30 minutes to 2 hours after ingesting milk or other dairy products. Some of these include:
- Abdominal pain and bloating
- Diarrhea
- Nausea
- Flatulence (passing gas)
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What does the test result mean?
Hydrogen breath test
A baseline breath sample is taken before giving a lactose-loaded drink. If the hydrogen gas in a person's breath significantly increases from the baseline, then it is likely that the person is lactose-intolerant.If the breath samples are negative or low for hydrogen, then it is less likely that the person is lactose-intolerant. The signs and symptoms may be due to another cause. However, some people may have lactose intolerance even with a negative result. In these cases, the bacteria in the intestine may not produce hydrogen. This can be confirmed after ingestion of lactulose, a synthetic, non-digestible disaccharide sugar that is similarly broken down to hydrogen gas by intestinal bacteria. Since lactulose is not absorbed by the intestine, the ongoing lack of hydrogen gas production suggests a false negative indicating the person may still be lactose-intolerant.
Glucose blood test
Timed samples of blood are taken and measured for glucose. If the glucose levels do not increase and the person has symptoms consistent with lactose intolerance, then the condition is likely present. Increasing blood glucose levels over the course of the test indicates that signs and symptoms are unlikely due to lactose intolerance.Care must be taken when interpreting results of the test. People who have diabetes may have an increase in blood glucose even when they do not produce enough lactase.
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Is there anything else I should know?
Antibiotics taken within the last month or two prior to testing may decrease the number of normal bacteria in the large intestine and give a false-negative hydrogen breath test.
If food moves more quickly than usual through a person's intestinal tract, that person may experience symptoms suggestive of lactose intolerance because the lactose has a shorter amount of time to be exposed to and broken down by lactase.
Bacterial overgrowth in the intestines (more bacteria present than normal) can cause symptoms similar to lactose intolerance, as can a variety of other gastrointestinal disorders.
Although it is not commonly done, it is possible to test for mutations in the gene that regulates lactase production (the LCT gene). Potentially, this could identify likely lactase deficiency and take the place of hydrogen breath testing.
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Should everyone have lactose tolerance testing?
Many people have some degree of lactose intolerance, especially as they age, but general testing is not considered necessary.
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Is the breath test used for other things?
Yes, other sugar "loads" can be given to examine other sugar (disaccharide) intolerances; however, lactose is the most commonly tested.
Other breath tests are available to help detect conditions, but they measure different substances and are unrelated to tolerance testing. Two examples are a breath test for Helicobacter pylori infection and alcohol (ethanol) testing.
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Can I do anything to increase my production of lactase?
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Is there treatment available for lactose intolerance?
There is no specific treatment to cure lactose intolerance, but it can be managed. Lactose-reduced dairy products are available for those with the condition. Supplements that contain the lactase enzyme can be taken when dairy products are consumed to help break down the lactose and prevent signs and symptoms. Non-dairy sources of calcium and other nutrients found in dairy products are also available for those who cannot tolerate lactose.
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Does lactose intolerance only apply to breast milk and cow's milk?
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Does soy milk have lactose in it?