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The Test Sample
What is being tested?
Intrinsic factor is a protein produced by a type of specialized cells that line the stomach wall known as parietal cells. During digestion, stomach acids release vitamin B12 from food and bind to intrinsic factor to form a complex. The formation of this complex is necessary for the absorption of vitamin B12 in the small intestine.
Among having functional roles in the brain and nervous system, vitamin B12 is important in the production of red blood cells. Without sufficient intrinsic factor, vitamin B12 goes largely unabsorbed and the body cannot produce enough normal red blood cells, leading to anemia. Besides anemia, decrease in the numbers of neutrophils and platelets (neutropenia, thrombocytopenia) may also occur.
Anemia that is due to a lack of intrinsic factor is called pernicious anemia. This is primarily an autoimmune condition that occurs when the body's immune system targets its own tissues and develops antibodies directed against the parietal cells and/or the intrinsic factor. These antibodies can damage the parietal cells and disrupt intrinsic factor production or prevent intrinsic factor from carrying out its biological function.
Two types of IF antibodies can be tested by the laboratory:
- Intrinsic factor blocking antibody (type 1), which is more specific for pernicious anemia and is the one that is usually tested.
- Intrinsic factor binding antibody (type 2), which interferes with the uptake of the vitamin B12-instrinsic factor complex.
For more on these, see the next tab, "The Test."
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein of the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
If you receive a vitamin B12 injection, you should wait 48 hours before having your blood drawn to reduce the risk of having a false-negative test result. Some healthcare providers may prefer not to draw a blood sample for the test within 2 weeks of an injection.