Intrinsic Factor Antibodies

Intrinsic Factor Antibodies

Synonym/acronym: IF antibodies, intrinsic factor blocking antibodies.

Common use

To assist in the investigation of suspected pernicious anemia.

Specimen

Serum (1 mL) collected in a gold-, red-, or red/gray-top tube. Place separated serum into a standard transport tube within 2 hr of collection.

Normal findings

(Method: Immunoassay) Negative.

Description

Intrinsic factor (IF) is a glycoprotein produced by the parietal cells of the gastric mucosa. IF is required for the normal absorption of vitamin B12 and measurement of circulating antibodies to IF is used to evaluate conditions of vitamin B12 deficiency. There are two types of antibodies: type 1, the more commonly present blocking antibody, and type 2, the binding antibody. The blocking antibody prevents attachment of vitamin B12 at the binding site of IF. Binding antibody combines with either free or complexed IF, inhibiting attachment of the vitamin B12-intrinsic factor complex to ileal receptors. Autoantibodies may also form against parietal cells and can be detected by enzyme immunoassay.

This procedure is contraindicated for

    N/A

Indications

  • Assist in the diagnosis of pernicious anemia
  • Evaluate patients with decreased vitamin B12 levels

Potential diagnosis

Increased in

  • Conditions that involve the production of these blocking and binding autoantibodies

  • Megaloblastic anemia
  • Pernicious anemia
  • Some patients with hyperthyroidism
  • Some patients with insulin-dependent (type 1) diabetes

Decreased in

    N/A

Critical findings

    N/A

Interfering factors

  • Recent treatment with methotrexate or another folic acid antagonist can interfere with test results.
  • Vitamin B12 injected or ingested within 48 hr of the test invalidates results.
  • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in assessing for anemia.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex. Central nervous system changes have a strong association with pernicious and megaloblastic anemias. Onset of the anemia may occur over a prolonged period of time during which the patient may be unaware of the development of symptoms; ask the patient whether he or she has experienced alterations in sensory organ function such as blurred or other changes in vision, loss of hearing, or changes in how foods taste. Ask the patient if he or she is experiencing dizziness, disorientation, irritability, memory loss, numbness, tingling, or lack of coordination. Ask male patients if they are experiencing impotence.
  • Obtain a history of the patient’s gastrointestinal and hematopoietic systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Note any recent procedures that can interfere with test results.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food or fluid restrictions unless by medical direction. Administration of vitamin B12, injected, ingested, or administered otherwise (e.g., absorbed by nasal gel or sublingual tablet), should be withheld within 2 wk before testing.

Intratest

  • Potential complications: N/A
  • Ensure that vitamin B12 has been withheld within 2 wk before testing.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family. The anemias associated with vitamin B12 deficiency produce a variety of signs and symptoms that may cause significant distress for the patient and family. Neurological complications may cause personality changes such as irritability, paranoia, disorientation, or delirium. Depending on the family situation, arrangements for social service or home care referrals may be indicated. Suggest ways to help the patient with fine motor deficits to feel greater independence, for example, the patient may have an easier time dressing if clothing without small buttons or hooks is chosen. If the patient has experienced permanent neurological deficits, the HCP may recommend a referral to physical therapy for rehabilitation. Instruct the patient to self-administer a vitamin B12 injection and provide resources for education regarding side effects and interactions with other drugs. Discuss the need for a well-balanced diet, foods that contain vitamin B12, and describe adequate daily fluid volume. Because there is an association between pernicious anemia and increased risk for developing gastric carcinoma, encourage the patient to have regular complete physical examinations.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include antibodies antithyroglobulin and antithyroid peroxidase, biopsy bone marrow, CBC, CBC RBC indices, folic acid, and vitamin B12.
  • Refer to the Gastrointestinal and Hematopoietic systems tables at the end of the book for related tests by body system.
References in periodicals archive ?
Patients who produce Intrinsic Factor but who then also produce autoimmune Intrinsic Factor Antibodies are diagnosed as having Pernicious Anaemia or more correctly Autoimmune Metaplastic Atrophic Gastritis.
The test currently used to identify any Intrinsic Factor Antibodies is the Competitive Binding Luminescence Assay and it's woefully inadequate to the extent that the new Guidelines suggest that if the test for the IF antibody is positive then the patient will have Pernicious Anaemia; however, if the test is negative for the antibody and the patient has the symptoms of the disease then he or she should be diagnosed as having Negative Intrinsic Factor Antibody Pernicious Anaemia.
23 All patients with PA were positive for parietal cell and intrinsic factor antibodies.
Detecting the presence of intrinsic factor autoantibodies in patients with vitamin B12 deficiency is considered fairly diagnostic of chronic gastritis and pernicious anemia (1) as it is rare to find intrinsic factor antibodies associated with other conditions (2).
Manufacturers of automated vitamin B12 assays recommend that patients be tested for intrinsic factor antibodies if test results for serum vitamin B12 conflict with the clinical diagnosis.
AGPA are a marker of autoimmune gastritis whereas intrinsic factor antibodies are associated with pernicious anemia.
Even though ELISA has advantages over RIA, not all ELISA methods of detecting intrinsic factor antibodies may be the same as they relate to the purity of the antigen and the antigenisity of the preparation.
In the group of 21 patients with Cbl levels from 201 to 299 pg/mL, 2 had peripheral neuropathy, 2 had positive intrinsic factor antibodies, and 8 had elevated fasting gastrin levels.
In our study, 1 patient in the group with Cbl levels of [is less than or equal to] 200 pg/mL and 2 patients from the other group had positive intrinsic factor antibodies.
A low vitamin B12 can be due to a number of causes including malabsorption, intrinsic factor antibodies, insufficient dietary intake, and autoimmune disorders.
Two types of intrinsic factor antibodies are known to exist:
Specificity of the test is very high because intrinsic factor antibodies are extremely rare in cases where B12 deficiency is not caused by pernicious anemia.