Intrinsic factor Antibody (IF Ab)

Sample

1. The serum the patient is needed.
2. This test can also be done on the plasma.
3. The sample is stable for 4 hours at room temp.
4. By refrigerating the sample is stable for 3 days.

Purpose of the test (Indication) for Intrinsic factor Antibody

• To diagnose pernicious anemia.

Precautions for Intrinsic factor Antibody

1. Avoid injection of vit.B12 within 48 hours of testing.

Pathophysiology of Intrinsic factor Antibody

1. Megaloblastic anemia is due to a deficiency of vit.B12 which is the major cause.
2. Intrinsic factor is secreted in the stomach and this is needed for the absorption of the vit. B12.
   1. The intrinsic factor is the protein produced by the parietal cells.

1. 2. Antibodies against the intrinsic factor are produced by the activation of the immune system.

Mechanism of Pernicious anemia:

1. In Megaloblastic anemia IF is decreased or absent.
   1. This is one of the autoimmune diseases.
2. IF Ab is found in a high percentage of children with juvenile pernicious anemia.
   1. IF Ab is 50 to 75% positive in these patients.
3. IF Ab is of two types :
   1. Type 1 blocking Ab which is more common blocks the binding of vit. B12 to IF. It is found in the serum of pernicious anemia cases around 40% to 50%.
   2. Type II binding antibody binds with the site on the intrinsic factor and is away from the vit. B12 site. These are found in 40% of the pernicious anemia cases.
      1. The second antibody is less common which affects the binding of IF in the ileum.
4. Positive IF Ab is confirmatory and is the cause of the disease.
5. Negative IF Ab does not rule out megaloblastic anemia because 50% of the patient does not show this antibody.
   1. For the diagnosis of Pernicious anemia, can supplement IF Ab with an anti-parietal antibody test.

6. Pernicious anemia rarely needs the vit.B12 absorption test called the Schilling test.
7. The testing of the intrinsic factor antibody and the anti-parietal antibodies is easier, quick, and more accurate.

Normal

• Intrinsic factor  antibody = Negative.

Positive test

1. Increased IF Ab is seen in a patient with pernicious anemia.
2. The IF antibodies are present in 3 to 6% of hyperthyroidism and insulin-dependent diabetes.

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