Lactose Tolerance Tests
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- Also Known As:
- Lactose Intolerance Test
- Hydrogen Breath Test
- Lactose Breath Test
- Disaccharide Absorption Test
- Oral Lactose Tolerance

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At a Glance
Why Get Tested?
To help diagnose lactose intolerance in individuals who have difficulty digesting dairy products, or sometimes as part of an investigation of malabsorption, which is difficulty digesting food and absorbing nutrients from food
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.
What is being tested?
Lactose tolerance tests measure hydrogen in the breath or changes in the level of glucose in the blood after a person is given a drink containing a standard amount of lactose, thus determining whether the individual is capable of proper digestion of lactose.
Lactose is a sugar with a complex structure (a disaccharide). It is found in milk and many other dairy products. Before it can be absorbed and used by the body, it must be broken down into two simpler sugars, glucose and galactose (monosaccharides). This digestion step is performed by lactase, an enzyme produced by cells lining the small intestine.
If an individual does not produce enough lactase (lactase deficient), then undigested lactose passes through the small intestine to the large intestine, where bacteria break it down, producing hydrogen gas and lactic acid. This process can cause the affected person to experience abdominal pain and bloating, flatulence (passing gas), and diarrhea within 30 minutes to 2 hours of consuming milk or other dairy products.
Almost all babies are born with the ability to digest lactose, but lactase production normally decreases as an individual ages. About 65-70% of the world’s population develops some degree of lactose intolerance by the time they reach adulthood. The intolerance can vary by race and ethnicity. While only about 5% of northern Europeans are lactose intolerant, more than 90% of Asians and Native Americans become lactose intolerant.
Two different types of lactose tolerance tests are available. In both of these, the person tested is given a liquid to drink that contains a standard amount of lactose. A sample for testing is taken immediately before, and a series of timed samples is collected at intervals after taking the lactose drink.
Hydrogen breath test
This is the test more commonly used to detect and diagnose lactose intolerance. This test measures hydrogen gas in breath samples taken before and after the lactose drink. With lactose intolerance, undigested lactose reaches the large intestine and is broken down by bacteria, producing excess hydrogen gas. The hydrogen gas enters the circulation and is eventually exhaled by the lungs and can be measured in the breath.
Glucose blood test
This is an alternate test sometimes used to detect and diagnose lactose intolerance. This test measures the glucose level in the blood samples taken immediately before and after the lactose drink. Since lactose is normally broken down to glucose and galactose, taking the lactose drink would normally lead to absorption of this glucose and result in an increase in blood glucose. In persons with lactose intolerance, there is inadequate breakdown of lactose and so this rise in blood glucose is not seen.
How is the sample collected for testing?
Breath samples are collected by blowing into a bag or other collection device. Blood samples are obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
Fasting is required before and during testing, and you must be off antibiotics and stomach medications, such as antacids, laxatives and stool softeners, for two weeks prior to the test. There are other medications that may interfere with the test, so consult your healthcare practitioner about the medications you are taking. You should also not exercise or smoke for several hours before testing. In some cases, additional instructions may be provided by the health practitioner and/or laboratory. For example, you may be asked to brush your teeth and then rinse your mouth with water prior to the hydrogen breath test and then again after drinking the liquid containing lactose. Follow any instructions you are given.
Common Questions
View Sources
Sources Used in Current Review
Roy, P.K. 2015. Medscape. Lactose Intolerance. Available online at http://emedicine.medscape.com/article/187249-overview. Accessed Nov. 26, 2016.
NIH. U.S. National Library of Medicine. 2016. Lactose Intolerance. Available online at https://ghr.nlm.nih.gov/condition/lactose-intolerance. Accessed Nov. 26, 2016.
Rodriguez, R. 2012. The NCMHD Center of Excellence for Nutritional Genomics. Information – Concepts in Nutrigenomics – Lactose Intolerance. Available online at http://nutrigenomics.ucdavis.edu/?page=information/Concepts_in_Nutrigenomics/Lactose_Intolerance. Accessed Nov. 28, 2016.
University of Michigan Health System. 2015. Hydrogen Breath Test. Available online at http://www.med.umich.edu/1libr/aha/umhbt.htm. Accessed Nov. 27, 2016.
Sources Used in Previous Reviews
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Delgado, J. and Grenache, D. (Updated 2011 November). Malabsorption. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/Malabsorption.html?client_ID=LTD#tabs=0. Accessed July 2012.
Mayo Clinic staff (2012 April 4). Lactose intolerance. MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/lactose-intolerance/DS00530/METHOD=print. Accessed July 2012.
Zieve, D. and Eltz, D. (Updated 2012 April 16). Lactose intolerance. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000276.htm. Accessed July 2012.
Roy, P. et. al. (Updated 2011 June 16). Lactose Intolerance. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/187249-overview. Accessed July 2012.
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(2009 November 7). Hydrogen Breath Test. University of Michigan Health System [On-line information]. Available online at http://www.med.umich.edu/1libr/aha/umhbt.htm. Accessed July 2012.
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Lomer, M. et. al. (2008 January 23). Review Article: Lactose Intolerance in Clinical Practice – Myths and Realities. Medscape Today News from Alimentary Pharmacology & Therapeutics. V 27(2):93-103 [On-line information]. Available online at http://www.medscape.com/viewarticle/568556. Accessed July 2012.
Zhao, J. et. al. (2010 May 20). Lactose Intolerance in Patients with Chronic Functional Diarrhoea: The Role of Small Intestinal Bacterial Overgrowth. Medscape Today News from Alimentary Pharmacology & Therapeutics. V 31(8):892-900 [On-line information]. Available online at http://www.medscape.com/viewarticle/719417. Accessed July 2012.
Swagerty, D. et. al. (2002 May 1). Lactose Intolerance. Am Fam Physician. 2002 May 1;65(9):1845-1851. [On-line information]. Available online at http://www.aafp.org/afp/2002/0501/p1845.html. Accessed July 2012.
Marks, J. (Reviewed 2009 February 10). Hydrogen Breath Test. MedicineNet.com. [On-line information]. Available online at http://www.medicinenet.com/hydrogen_breath_test/article.htm. Accessed July 2012.
Simre’n, M. and Stotzer, P. (2006 March). Use and abuse of hydrogen breath tests. Gut 2006;55:297–303. [On-line information]. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1856094/. Accessed July 2012.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 350-351, 656-657.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. 4th edition, St. Louis: Elsevier Saunders; 2006, Pp 1862-1864.
Woodfin BM, Arora S: Lactose Intolerance, in Clinical Studies in Medical Biochemistry. Glew RH and Iinomiya Y, eds. Oxford University Press:New York. Chapter 14, Pp 152-160, 1997.
Hack S, Bergwerk A. Lactose Intolerance, in Pediatric Nutrition in Chronic Diseases and Developmental Disorders, 2nd ed. Walberg Ekvall S and Ekvall VK, eds. Oxford University Press: New York. Chapter 50, Pp 340-345, 2005.
Gerbault P, Liebert A, Itan Y, et. al. Evolution of lactose persistence: an example of human niche construction. Phil Trans R Soc B, 366:863-877, 2011.
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