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Medical Author:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• What is the lactose tolerance test?
• What is lactose intolerance?
• How is the lactose tolerance test done?
• What other tests can detect lactose intolerance?
• Find a local Gastroenterologist in your town
• Lactose Tolerance Test Index

How is the lactose tolerance test done?

The lactose tolerance test requires an individual to drink a liquid that contains lactose. In the small intestine among lactose tolerant individuals, the ingested lactose is split into galactose and glucose which then are absorbed from the intestine and go into the blood. Several blood samples are taken over a two hour period following the ingestion of the lactose to measure the blood glucose level. If lactose tolerance is normal, the glucose level in the blood rises due to the absorption of glucose from the intestine. If there is lactose intolerance, the glucose level does not rise.

What other tests can detect lactose intolerance?

Other tests used to detect lactose intolerance include the lactose hydrogen breath test and stool acidity test, the latter is primarily used in infants and very young children. There also is a genetic test which can determine whether an individual has or does not have the intestinal enzyme that is required for the digestion and absorption of lactose.