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Test ID: IFBA Intrinsic Factor Blocking Antibody, Serum

Reporting Name

Intrinsic Factor Blocking Ab, S

Useful For

Confirming the diagnosis of pernicious anemia

Clinical Information

The cobalamins, also referred to as vitamin B12, are a group of closely related enzymatic cofactors involved in the conversion of methylmalonyl-coenzyme A to succinyl-coenzyme A and in the synthesis of methionine from homocysteine. Vitamin B12 deficiency can lead to megaloblastic anemia and neurological deficits. The latter may exist without anemia, or precede it. Adequate replacement therapy will generally improve or cure cobalamin deficiency. Unfortunately, many other conditions, which require different interventions, can mimic the symptoms and signs of vitamin B12 deficiency. Moreover, even when cobalamin deficiency has been established, clinical improvement may require different dosages or routes of vitamin B12 replacement, depending on the underlying cause. In particular, patients with pernicious anemia (PA), possibly the commonest type of cobalamin deficiency in developed countries, require either massive doses of oral vitamin B12 or parenteral replacement therapy. The reason is that in PA patients suffer from gastric mucosal atrophy, most likely caused by a destructive autoimmune process. This results in diminished or absent gastric acid, pepsin and intrinsic factor (IF) production. Gastric acid and pepsin are required for liberation of cobalamin from binding proteins, while IF binds the free vitamin B12, carries it to receptors on the ileal mucosa, and facilitates its absorption. Most PA patients have autoantibodies against gastric parietal cells or intrinsic factor, with the latter being very specific but only present in approximately 50% of cases. By contrast, parietal cell antibodies are found in approximately 90% of PA patients, but are also found in a significant proportion of patients with other autoimmune diseases, and in approximately 2.5% (4th decade of life) to approximately 10% (8th decade of life) of healthy individuals.


The aim of the work-up of patients with suspected vitamin B12 deficiency is to first confirm the presence of deficiency and then to establish its most likely etiology.


Measurement of serum vitamin B12, either preceded or followed by serum methylmalonic acid measurement, is the first step in diagnosing pernicious anemia (PA). If these tests support deficiency, then intrinsic factor blocking antibody (IFBA) testing is indicated to confirm PA as the etiology. A positive IFBA test supports very strongly a diagnosis of PA. Since the diagnostic sensitivity of IFBA testing for PA is only around 50%, an indeterminate or negative IFBA test does not exclude the diagnosis of PA. In these patients, either PA or another etiology, such as malnutrition, may be present. Measurement of serum gastrin levels will help in these cases. In patients with PA, fasting serum gastrin is elevated to more than 200 pg/mL in an attempted compensatory response to the achlorhydria seen in this condition.


For a detailed overview of the optimal testing strategies in PA diagnosis, see ACASM / Pernicious Anemia Cascade, Serum and associated Vitamin B12 Deficiency Evaluation in Special Instructions.

Testing Algorithm

See Vitamin B12 Deficiency Evaluation in Special Instructions.

Analytic Time

Same day/1 day

Day(s) and Time(s) Performed

Monday through Friday; 6 a.m.-12 a.m.

Saturday; 6 a.m.-6 p.m.

Clinical Reference

1. Toh BH, Van Driel IR, Gleeson PA: Pernicious anemia. N Engl J Med 1997;337:1441-1448

2. Klee GG: Cobalamin and folate evaluation: measurement of methylmalonic acid and homocysteine vs vitamin B12 and folate. Clin Chem 2000;46:1277-1283

3. Ward PC: Modern approaches to the investigation of vitamin B12 deficiency. Clin Lab Med 2002:22;435-445

4. Stabler SP, Allen RH: Vitamin B12 deficiency as a worldwide problem. Ann Rev Nutr 2004;24:299-326

5. Roberts NB, Taylor A, Sodi R: Chapter 37: Vitamins and trace elements. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Sixth edition. Edited by N Rafai, AR Horvath, CT Wittwer. Elsevier, 2018, pp 639-718

6. Bizzaro N, Antico A: Diagnosis and classification of pernicious anemia. Autoimmun Rev 2014;13(4-5):565-568

Method Name

Immunoenzymatic Assay

Specimen Type


Specimen Required

Patient Preparation: For patients receiving vitamin B12 injections wait a minimum of 2 weeks after last injection before obtaining specimen.


Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 1 mL

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 14 days
  Frozen  14 days

Special Instructions

Reference Values


Test Classification

This test has been cleared, approved or is exempt by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
IFBA Intrinsic Factor Blocking Ab, S 31444-3


Result ID Test Result Name Result LOINC Value
IFBLA Intrinsic Factor Blocking Ab, S 31444-3
CMT31 Comment 48767-8
Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Behavioral, mml-Movement-Disorders, mml-Demyelinating-Diseases, mml-Neuroimmunology, mml-Neuromuscular, mml-Pediatric, mml-Spinal-Cord, mml-Neurometabolic, mml-Neuro-ophthalmology