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Lactose Tolerance Blood Test

Last updated June 2, 2019

Approved by: Maulik P. Purohit MD, MPH

The Lactose Tolerance Blood Test helps determine if an individual is lactose intolerant.

What are other Names for this Test? (Equivalent Terms)

  • Lactose Blood Test
  • Lactose Intolerance Blood Test

What is Lactose Tolerance Blood Test? (Background Information)

  • Lactose is a disaccharide (combination of 2 sugars chemically attached to each other) that is composed of glucose and galactose
  • For the body to break down lactose, it requires the enzyme lactase. Lactase is produced in the intestines. It breaks lactose down into the simple sugars glucose and galactose. Certain foods, such as milk, are rich in lactose. Milk may contain up to 12 grams of lactose per serving
  • Individuals who are lactose intolerant may experience uncomfortable gastric symptoms as a result of their inability to produce lactase, and therefore have an inability to digest lactose
  • Lactose passes through the digestive tract intact in individuals who are lactose intolerant. Excess lactose in the intestines causes the unpleasant symptoms of lactose intolerance, including diarrhea and abdominal cramps. This is in part due to microorganisms in the gut feeding on the lactose
  • The Lactose Tolerance Blood Test helps determine if an individual is lactose intolerant. It is performed by ingesting a large amount of lactose and monitoring blood glucose levels to determine if the lactose is successfully being broken down

What are the Clinical Indications for performing the Lactose Tolerance Blood Test?

The clinical indicators for performing the Lactose Tolerance Blood Test include the following in response to ingestion of lactose-containing foods such as milk:

  • Diarrhea
  • Abdominal cramps
  • Flatus (passing gas)

How is the Specimen Collected for Lactose Tolerance Blood Test?

Following is the specimen collection process for Lactose Tolerance Blood Test:

Sample required: Blood 

Process of obtaining a blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Lactose Tolerance Blood Test Result?

  • A decreased glucose level (less than 20 mg/dl compared to fasting level) in blood after ingestion of lactose may point to a diagnosis of lactose intolerance

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • Not all dairy products are rich in lactose. Yogurt has undergone digestion by microorganisms, which has broken down the majority of lactose originally present in milk to glucose and galactose. Such foods may be more compatible with lactose intolerant individuals

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

The following DoveMed website link is a useful resource for additional information:


Please visit our Laboratory Procedures Center for more physician-approved health information:


References and Information Sources used for the Article:

Helpful Peer-Reviewed Medical Articles:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: June 3, 2016
Last updated: June 2, 2019