Intrinsic factor Ab

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.

Immunoassay.

Consult pathologist.

Diagnosis of pernicious anaemia.

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.