Intrinsic factor Antibody (IF-Ab)

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

1. The serum the patient 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.
5. For the assay of intrinsic factors (IF), aspiration of gastric juice is necessary.

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 a deficiency of vit.B12, the major cause.
2. Intrinsic factor is secreted in the stomach, which is needed to absorb the vit. B12.
   1. 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 50% to 70% positive in 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 pernicious anemia cases around 40% to 50%.
      1. Another reference states that this antibody is usually present in around 60% to 75% of pernicious anemia patients.
      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, affecting 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 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.

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% to 28% of patients with diabetes mellitus.
   4. 25% to 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 where 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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