Also Known As
Lactose Intolerance Test
Hydrogen Breath Test
Lactose Breath Test
Disaccharide Absorption Test
Oral Lactose Tolerance
Formal Name
Hydrogen Breath Test; Lactose Tolerance Test
This article was last reviewed on
This article waslast modified on December 30, 2017.
At a Glance
Why Get Tested?

To help diagnose lactose intolerance in individuals who have difficulties digesting dairy products, or sometimes as part of an investigation of malabsorption

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.

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

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 healthcare 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.

Accordion Title
Common Questions
  • 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.

  • 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)
  • 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.

  • 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.

  • 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.

  • 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.

  • Can I do anything to increase my production of lactase?

    No, lactase concentrations do not change with lifestyle changes. However, many people with lactose intolerance are able to digest small amounts of milk and are often able to tolerate yogurt and hard cheeses.

  • 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.

  • Does lactose intolerance only apply to breast milk and cow's milk?

    No, lactose is present in the milk of all mammals, including, for example, goat's milk.

  • Does soy milk have lactose in it?

    No. Most people with lactose intolerance can drink soy milk as well as other plant-based products, such as rice milk or almond milk.

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

Dugdale, D. (Updated 2010 July 7). Lactose tolerance tests. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003500.htm. Accessed July 2012.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 608-610.

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.

(Reviewed 2010 May). Lactose intolerance. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/condition/lactose-intolerance. Accessed July 2012.

(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.

(© 1995-2009). Lactose and Glucose Hydrogen Breath Test. Cleveland Clinic [On-line information]. Available online at http://my.clevelandclinic.org/disorders/Lactose_Intolerence/hic_Lactose_and_Glucose_Hydrogen_Breath_Test.aspx. Accessed July 2012.

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.

Ask a Laboratory Scientist

This form enables you to ask specific questions about lab tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science.

Disclaimer
Thank you for using the Consumer Information Response Service ("the Service") to inquire about the meaning of your lab test results.  The Service is provided free of charge by the American Society for Clinical Laboratory Science, which is one of many laboratory organizations that supports Lab Tests Online.
Please note that information provided through this free Service is not intended to be medical advice and should not be relied on as such. Although the laboratory provides the largest single source of objective, scientific data on patient status, it is only one part of a complex biological picture of health or disease. As professional clinical laboratory scientists, our goal is to assist you in understanding the purpose of laboratory tests and the general meaning of your laboratory results. It is important that you communicate with your physician so that together you can integrate the pertinent information, such as age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), to determine your health status. The information provided through this Service is not intended to substitute for such consultations with your physician nor specific medical advice to your health condition.
By submitting your question to this Service, you agree to waive, release, and hold harmless the American Society for Clinical Laboratory Science and its affiliates or their past or present officers, directors, employees, agents, and Service volunteers (collectively referred to as "ASCLS") and the American Association  for Clinical Chemistry and its affiliates or their past or present officers, directors, employees, agents, and Service volunteers (collectively referred to as "AACC") from any legal claims, rights, or causes of action you may have in connection with the responses provided to the questions that you submit to the Service.
AACC, ASCLS and its Service volunteers disclaim any liability arising out of your use of this Service or for any adverse outcome from your use of the information provided by this Service for any reason, including but not limited to any misunderstanding or misinterpretation of the information provided through this Service.