Test library
Lactose Breath and Blood Test
The Lactose Tolerance Test measures how blood glucose changes after a person drinks a lactose solution. It is used to evaluate lactose intolerance when digestive symptoms follow milk or dairy products.
Order Lactose Tolerance Test
Order online and visit a local collection site, or choose an at-home kit where available. No referral and no insurance required.
Order Lactose Tolerance Test- Typical turnaround
- 1-3 business days
- Starting price
- From $159
- Results
- Confidential, online
Quick answer
The Lactose Tolerance Test checks how the body handles lactose, the sugar found in milk. After a person drinks a measured lactose solution, blood glucose is measured over a period of time. If lactose is broken down normally, glucose rises; if the enzyme lactase is deficient, glucose may stay flat and digestive symptoms can appear. The test helps evaluate whether lactose intolerance explains symptoms after dairy.
What this test measures
Lactose is a sugar in milk and dairy products. It is digested by lactase, an enzyme in the small intestine. When lactase activity is low, undigested lactose passes into the colon, where bacteria ferment it and cause gas, bloating, cramps, and diarrhea.
During the test, a person drinks a lactose solution after a fasting period. Blood samples are taken at intervals to measure glucose, and the person reports any symptoms. A rise in glucose suggests lactose was digested, while a flat curve suggests malabsorption. Some providers also measure hydrogen in breath instead.
Providers order lactose testing when digestive symptoms follow milk, ice cream, or other dairy products, and when other causes have been considered. Lactose intolerance differs from milk allergy, which involves the immune system. A qualified healthcare provider should interpret the test and advise on diet changes.
- Fasting blood glucose
- Serial blood glucose after the lactose drink
- Change in blood glucose over the test period
- Symptom record during testing
- Hydrogen breath markers when a breath test is used
- Lactose dose and timing documentation
Why people order this test
- Evaluate digestive symptoms that follow dairy products
- Distinguish lactose intolerance from other causes
- Confirm a suspected lactase deficiency
- Add objective information to a dietary assessment
- Guide a clinician's advice on dairy intake
- Follow symptoms that persist despite dietary changes
How to prepare
Fasting is required for a lactose tolerance test, typically overnight. Follow the laboratory's instructions about how long to fast, and avoid smoking or strenuous exercise before the test unless told otherwise.
Understanding your results
Results are usually available within one to three business days. A normal glucose rise suggests lactose was digested, while a flat response suggests malabsorption, especially if symptoms occur during the test. A qualified healthcare provider should interpret the findings.
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Frequently Asked Questions
How does the lactose tolerance test work?
A lactose drink is given after fasting, and blood glucose is measured at intervals. The change in glucose and any symptoms during the test help show whether lactose is being digested.
How is this different from a milk allergy test?
Lactose intolerance involves digestion of milk sugar, while milk allergy involves an immune response to milk proteins. They have different causes, tests, and management.
Do I need to fast?
Yes, fasting is required, usually overnight. Follow the specific instructions provided with the test order.
What if I feel unwell during the test?
Tell the laboratory staff right away. Symptoms during the test are recorded and are part of the assessment.
Can lactose intolerance develop in adults?
Yes. Lactase activity often declines with age, and intolerance can appear in adulthood even in people who previously tolerated dairy.
Ready to get tested?
Order online and visit a collection site near you, or choose a mail-in kit. No referral and no insurance required.
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