Intrinsic factor antibodies - serum
Last updated: Friday, 02, April, 2004
5 mL blood in plain tube.
As recent vitamin B12 administration is associated with a high rate of false positive results the sample must be collected prior to commencing therapy or at least one week after vitamin B12 administration.
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Diagnosis of pernicious anaemia.
High specificity for pernicious anaemia and a positive result is sufficient to establish the diagnosis.
Sensitivity is low thus a negative result does not exclude the diagnosis of pernicious anaemia.
Type 1 (blocking) antibody prevents the attachment of vitamin B12 to intrinsic factor: present in 50-60% of patients with pernicious anaemia.
Type 2 (precipitating) antibody prevents attachment of the vitamin B12-intrinsic factor complex to ileal receptors: present in 30% of patients with pernicious anaemia, and only in those who also have Type 1 antibodies.
Immunoassay kits which rely on blocking function of antibodies are usually less sensitive.
Oh R et al. Am Fam Physician 2003; 67(5): 993-994.