Haematology

Name

Alternative name/Profile

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Investigation

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Notes

Important sample requirements for external users:

Please centrifuge and separate the serum. As the assay will not be completed within 24 hours, freeze serum at -20°C or colder before and during shipment.

Urgent analysis available on request

Samples should be taken >14 days post B12 injection to avoid false positive or false equivocal results.

Limitations of this assay:

Heterophilic antibodies in human serum can react with reagent immunoglobulins, interfering with in vitro immunoassays. Patients routinely exposed to animals or to animal serum products can be prone to this.

Please contact the laboratory 01 4162012 for further information regarding limitations of this assay.

Related links

https://pernicious-anaemia-society.org/articles/testing-for-pernicious-anaemia/

Intrinsic Factor is a 50-kDA glycoprotein and is secreted by the parietal cells of the stomach. It is necessary for absorption of Vitamin B12 in the intestines. After exit from the acidic environment of the stomach, Vitamin B12 is able to bind to Intrinsic Factor and via specific receptor mediated endocytosis in the ileal mucosa the B12 Intrinsic Factor complex enters the portal circulation.

Pernicious anaemia is the most common Vitamin B12 deficiency and is characterised by Vitamin B12 deficiency, megaloblastic anaemia, neuropathy and atrophic gastritis with intrinsic factor autoantibodies. Pernicious anaemia occurs as an end result to an autoimmune disease that destroys the gastric mucosa. First the parietal cells of the stomach, which produce Intrinsic Factor, are depleted. Second autoantibodies to Intrinsic Factor block the binding sites for Vitamin B12.

There are two types of Intrinsic Factor Antibodies. Type 1 (Intrinsic Factor blocking antibodies) which, blocks the binding site on intrinsic factor for Vitamin B12 and type 2 (Intrinsic Factor binding antibodies) which, target a different site on intrinsic factor and prevent the intrinsic factor-Vitamin B12 complex from attaching to the binding sites in the small intestine.

The presence of Intrinsic Factor Antibodies (IFAB) as well as megaloblastic anaemia and low serum vitamin B12 are diagnostic of pernicious anaemia. A positive Intrinsic Factor antibody result can exclude the need for further testing. The following autoimmune disease states are associated with pernicious anaemia and the presence of intrinsic factor antibodies: Hashimoto’s thyroiditis, insulin dependent diabetes mellitus, Grave’s disease, rheumatoid arthritis, myasthenia gravis, hypoparathyroidism and Lambert-Eaton syndrome.

Reference range

Positive, Negative or Equivocal

Last updated

Fri, 23 Jan 2026 08:29:05 GMT