What is Intrinsic Factor Antibody test?

Intrinsic factor antibody test helps in diagnosing pernicious anaemia, an autoimmune disease caused due to a deficiency of vitamin B12.

Intrinsic factor is a protein found in the wall of the stomach. It binds to vitamin B12 in the food and helps it get absorbed through the intestinal wall. 

However, in pernicious anaemia, the immune system produces antibodies (special proteins) against the intrinsic factor. These antibodies bind to the intrinsic factor protein and prevent the absorption of vitamin B12- intrinsic factor complex, leading to B12 deficiency. Lack of B12, in turn, causes improper development of RBCs and a shortage of red blood cells in the body.

Depending on the site of binding intrinsic factor antibodies are of two types:

  • Type 1 also called as intrinsic factor blocking antibodies: These antibodies block the binding site of vitamin B12 on the intrinsic factor 
  • Type 2 also known as intrinsic factor binding antibodies: These antibodies bind to a different site on the intrinsic factor (instead of B12 binding site) but they prevent the absorption of the B12-intrinsic factor complex into the intestines.
  1. Why is an Intrinsic Factor Antibody test performed?
  2. How do you prepare for an Intrinsic Factor Antibody test?
  3. How is an Intrinsic Factor Antibody test performed?
  4. What do Intrinsic Factor Antibody test results mean?

Intrinsic factor antibody test is considered as a confirmatory test for pernicious anaemia. It is performed only for patients who have tested positive for gastric parietal cells antibodies test, a screening test for pernicious anaemia.

In most cases, pernicious anaemia develops around the age of 60 and have the following mild symptoms:

Low vitamin B12 levels for a prolonged time may lead to damage in the nervous system, some of the symptoms of which are as follows:

If you have low vitamin B12 levels, your doctor may order this test to rule out pernicious anaemia.

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You do not need to fast for this test. Inform your doctor if you are consuming any prescription or non-prescription medicines, supplements or vitamins. If you recently had an injection of vitamin B12, you would have to wait for at least two weeks to have the test as the results will be affected by the injected vitamin.

A lab technician will withdraw a small amount of blood from a vein in your arm - you may feel a mild pricking sensation as the needle goes in. 

A few risks associated with this test are:

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Normal results:

Normal test results are written as negative. They indicate that you don’t have intrinsic factor antibodies in your blood.

Abnormal results:

Abnormal reading in this test is considered a positive result. It means that you have antibodies against the intrinsic factor in your blood.

Generally, type 1 antibodies are tested for as they are more specific for pernicious anaemia. Positive results indicate that you have the disease. 

It is important to note that only about 50% to 75% of the people suffering from pernicious anaemia show the presence of intrinsic factor antibodies. So your doctor would assess your overall condition to interpret the results.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

References

  1. South Tees Hospitals. NHS Foundation trust. National Health Service, U.K. Intrinsic factor antibodies
  2. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Intrinsic Factor Antibody
  3. Bunn HF. Approach to the anemias. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 158.
  4. Elghetany MT, Schexneider KI, Banki K. Erythrocytic disorders. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 32.
  5. Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 39.
  6. Pagana KD, Pagana TJ, Pagana TN. Intrinsic Factor Antibody. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. Pp:545.
  7. Oxford University Hospitals [internet]: NHS Foundation Trust. National Health Service. U.K., Intrinsic factor antibodies
  8. National Health Service [internet]. UK; Blood Tests
  9. Osborne, D., & Sobczynska-Malefora, A. Autoimmune mechanisms in pernicious anaemia & thyroid disease. Autoimmun Rev, 14(9), 763-768. PMID: 25936607
  10. Toh BH et al. Pernicious anemia. N Engl J Med. 1997 Nov 13;337(20):1441-8. PMID: 9358143
  11. Bizzaro, N., & Antico, A. (2014). Diagnosis and classification of pernicious anemia. Autoimmun Rev, 13(4-5), 565-568. PMID: 24424200

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