Test Catalog

Test ID: ACASM    
Pernicious Anemia Cascade, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of pernicious anemia


Diagnosis of vitamin B12 deficiency-associated neuropathy

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

If the vitamin B12 concentration is less than 150 ng/L, then the intrinsic factor blocking antibody (IFBA) test is performed. If IFBA result is negative or indeterminate, then the gastrin test is performed.

If the vitamin B12 concentration is 150 to 400 ng/L, then the methylmalonic acid (MMA) test is performed. If the MMA result is greater than 0.40 nmol/mL, then the IFBA test is performed.


See Vitamin B12 Deficiency Evaluation in Special Instructions.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Vitamin B12 deficiency can be caused by many factors, one of which is pernicious anemia, a condition resulting in deficient production of intrinsic factor in the parietal cells of the stomach. Intrinsic factor is a protein that is needed to assist in the absorption of vitamin B12 into the small intestine. Vitamin B12 is converted into adenosylcobalamin, which converts L-methylmalonic acid to succinyl coenzyme A; hence, a decrease in vitamin B12 absorption in the intestine can cause an excess of methylmalonic acid within the body.


Vitamin B12 deficiency may present with any combination of the following: macrocytic anemia, glossitis (painful inflammation of the tongue), peripheral neuropathy, weakness, hyperreflexia, ataxia, loss of proprioception, poor coordination, and affective behavioral changes. These manifestations may occur in any combination; many patients present with neurologic symptoms without macrocytic anemia.


A group of tests is often required to establish the correct diagnosis as determination of vitamin B12 in serum does not detect all cases of vitamin B12 deficiency. Mayo Clinic's Department of Laboratory Medicine and Pathology offers a diagnostic algorithm to expedite the identification of patients with vitamin B12 deficiency. This algorithm takes into account the following facts:

-The most sensitive test for vitamin B12 deficiency at the cellular level is the assay for methylmalonic acid (MMA).

-Nearly half of the cases of pernicious anemia can be unambiguously identified if the serum test for intrinsic factor blocking antibody is positive (this is a simpler and less expensive test than the MMA).

-Serum gastrin is usually markedly increased in pernicious anemia (as a result of gastric atrophy) and this test can be used as a substitute for the more complicated and more expensive Schilling test of intestinal absorption of vitamin B12.


The algorithm is similar to that published,(1) except that the serum gastrin assay is performed in place of the Schilling test. Experience with both Mayo Clinic and Mayo Clinic Laboratories' cases has corroborated that this is a cost-effective alternative to the Schilling test.


In our experience, greater than 90% of laboratory test costs can be saved by using the algorithm rather than ordering all of the services for a patient suspected of having B12 deficiency. Furthermore, the substitution of the serum gastrin assay for the Schilling test offers 3 advantages:

1. It is an in vitro test that does not require administration of radioisotopes to patients

2. It can be performed on mailed-in specimens

3. It is much less expensive


Only those tests that are appropriate, as defined by the algorithm, will be performed.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

180-914 ng/L

Interpretation Provides information to assist in interpretation of the test results

Vitamin B12 >400 ng/L

Results do not suggest B12 deficiency-no further testing.

Vitamin B12 150 to 400 ng/L

Borderline vitamin B12 level-methylmalonic acid (MMA) is performed. If MMA is >0.40 nmol/mL, then intrinsic factor blocking antibody (IFBA) is performed.

Vitamin B12 <150 ng/L

Vitamin B12 deficiency-IFBA is performed. If IFBA is negative or indeterminate, then gastrin is performed.

MMA < or =0.40 nmol/mL

This value implies that there is no vitamin B12 deficiency at the cellular level.

IFBA positive

Consistent with pernicious anemia, Graves disease, or Hashimoto thyroiditis.

Gastrin >200 pg/mL

Result consistent with pernicious anemia.

Gastrin <200 pg/mL

Result does not suggest pernicious anemia.


See Vitamin B12 Deficiency Evaluation in Special Instructions.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Many other conditions are known to cause an increase or decrease in the serum vitamin B12 concentration and should be considered in the interpretation of the assay results, including:

Increased serum vitamin B12

Decreased serum vitamin B12

Ingestion of vitamin C


Ingestion of estrogens


Ingestion of vitamin A


Hepatocellular injury


Myeloproliferative disorder

Ethanol ingestion


Contraceptive hormones






Multiple myeloma


Some patients exposed to animal antigens, either in the environment or as part of treatment or imaging procedure, may have circulating antianimal antibodies present. These antibodies may interfere with the vitamin B 12 assay reagents to produce unreliable results.


Some patients with other autoimmune diseases may have positive intrinsic factor blocking antibody (IFBA) assays without suffering from pernicious anemia (PA). This is reported particularly in patients with autoimmune thyroid disease or type I diabetes mellitus. In the validation of this assay, 24 individuals with these autoimmune endocrine diseases were tested and all were IFBA negative. However, 5 of 15 of patients with rheumatoid arthritis were IFBA positive during the validation of this assay. The literature suggests such individuals may, in fact, be at risk of later development of PA.


Since the IFBA test is competitive binding assay, the risk of heterophile antibody interference is low. During validation, 24 human antimouse antibody positive specimens and 25 specimens with other heterophile antibodies were tested and all were IFBA negative. However, if the clinical picture does not agree with the IFBA test result, the laboratory should be consulted for advice.


Isolated serum gastrin levels can only be interpreted in fasting patients; nonfasting specimens are uninterpretable.


Artifactual hypergastrinemia may be observed in fasting patients who have undergone procedures that result in temporary gastric distention or dysmotility (eg, after gastroscopy).


Renal failure prolongs the serum half-life of gastrin and is associated with increased serum gastrin levels.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Green R, Kinsella LJ: Current concepts in the diagnosis of cobalamin deficiency. Neurology. 1995 Aug;45(8):1435-1440

2. Lahner E, Annibale B: Pernicious anemia: new insights from a gastroenterological point of view. World J Gastroenterol. 2009 Nov 7;15(41):5121-5128

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

4. Toh BH: Pathophysiology and laboratory diagnosis of pernicious anemia. Immunol Res. 2017 Feb;65(1):326-330

Special Instructions Library of PDFs including pertinent information and forms related to the test