Intrinsic factor Ab

Keywords: Intrinsic factor antibody, IFA

Specimen:

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.

Method:

Immunoassay.

Reference Interval:

Consult pathologist.

Application:

Diagnosis of pernicious anaemia.

Interpretation:

High specificity for pernicious anaemia. 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.

Reference:

Oh R et al. Am Fam Physician. 2003; 67(5): 993-994.