The Test Sample
What is being tested?
This test detects intrinsic factor antibody in the blood. Intrinsic factor (IF) is a protein produced by a type of specialized cells that line the stomach wall known as parietal cells that is required for the absorption of vitamin B12 from the diet. During digestion, stomach acids release vitamin B12 from food and intrinsic factor binds to the vitamin B12 and allows it to be absorbed at a specific segment of the small intestine. Among other functions, 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 condition occurs primarily 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 function.
There are two types of intrinsic factor antibodies: intrinsic factor blocking antibody, which blocks the binding of vitamin B12 to intrinsic factor, and intrinsic factor binding antibody, which binds to the vitamin B12-instrinsic factor complex. The intrinsic factor blocking antibody is more specific for pernicious anemia and is the one that is usually tested.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in 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 for this test. The doctor may prefer not to draw a blood sample for the test within 2 weeks of an injection.