Intrinsic Factor Antibody (IF-Ab)

What sample is needed for Intrinsic Factor Antibody (IF-Ab)?

1. The patient’s serum is needed.
2. This test can also be done on the plasma.
3. The sample is stable for 4 hours at room temp.
4. When refrigerated, the sample remains stable for 3 days.
5. For the assay of intrinsic factors (IF), gastric juice aspiration is required.

What are the Indications for Intrinsic factor Antibody (IF-Ab)?

• To diagnose pernicious anemia.

What are the precautions for Intrinsic Factor Antibody (IF-Ab)?

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

What is the mechanism of megaloblastic anemia?

1. Megaloblastic anemia is due to vitamin B12 deficiency, the major cause.
2. Intrinsic factor is secreted in the stomach, which is needed to absorb the vit. B12.
3. The intrinsic factor is the protein produced by the parietal cells.

3. The activation of the immune system produces antibodies against the intrinsic factor.

What is the mechanism of Pernicious anemia?

1. In Megaloblastic anemia, IF is decreased or absent.
   1. This may be due to autoimmune diseases.
2. IF-Ab is found in a high percentage of children with juvenile pernicious anemia.
   1. IF-Ab is positive in 50% to 70% of patients with pernicious anemia.
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 patients with pernicious anemia at around 40% to 50%.
      1. Another reference states that this antibody is typically present in 60% to 75% of patients with pernicious anemia.
      2. This antibody is diagnostic of pernicious anemia.
   2. Type II binding Ab (antibody) binds with the site on the intrinsic factor and is away from the vit. B12 site or combined with IF + Vitamin B12 complex.
      1. These are found in 40% of the pernicious anemia cases.
      2. The second antibody is less common and affects IF binding in the ileum.
4. A positive IF-Ab is confirmatory and indicates the cause of the disease.
5. A negative IF-Ab does not rule out megaloblastic anemia because 50% of patients do not show this antibody.
6. One can supplement IF-Ab with an anti-parietal antibody test to diagnose Pernicious anemia.

7. Pernicious anemia rarely needs the vit B12 absorption test called the Schilling test.
8. Testing the intrinsic factor antibody and the anti-parietal antibodies is easier, quicker, and more accurate.
9. False-positive result:
   1. False-positive results are reported in diabetes mellitus, adrenal insufficiency, thyroid diseases, and various gastric abnormalities.

What do you know about Anti-parietal cell antibody?

1. It is detected in 76% to 91% of the cases with pernicious anemia.
2. It is much more nonspecific than the IF-Ab test.
3. It is found in:
   1. 5% to 10% of the normal person.
   2. 30% to 60% of the patients with idiopathic atrophic gastritis.
   3. 12%-28% of patients with diabetes mellitus.
   4. 25%-35% of patients with thyrotoxicosis.
   5. 25% of the patients with Hashimoto’s thyroiditis.

What is the normal value of Intrinsic Factor Antibody (IF Ab)?

• Intrinsic factor antibody = Negative.

What are the conditions under which a Positive test for Intrinsic Factor Antibody (IF-Ab)?

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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