Haematology

Name

Alternative name/Profile

Department

Investigation

Specimen type

Sample type

Sample container & volume

Frequency of analysis

Turnaround time

Availability

Notes

Total B12 assay now performed on Abbott Alinity i platform  as of 10th September 2024. Note new reference range.

Patient must be fasting for a minimum of 12hrs

(Queries to Haematinics Laboratory on 01-4162012)

See GP External Request Form for B12 and Folate. This form must be filled in completely. When requesting blood tests for patients, place all extra forms (e.g. for B12/Folate and Vit D) and necessary samples in the same bag to allow easier processing of patient samples on receipt in laboratory.

All forms may be found here:

https://www.stjames.ie/services/laboratorymedicinelabmed/policiesandguidelines/gpexternalrequestforms/

Haematinics Demand Management Guidelines:

1) Patients on parenteral vitamin B12 or oral folic acid replacement therapy should not have further vitamin B12 or folic acid measurements performed unless blood counts or neurological symptoms fail to improve.

2) Repeating normal vitamin B12 levels is rarely indicated within 6 months of testing.

3) Repeating normal folate levels is rarely indicated within 3 months of testing.

4) Clinical details are required for all vitamin B12 and folate requests. 

Limitations of this Assay:

• Results should be used in conjunction with other data e.g. symptoms, results of other tests, and clinical impressions.
• The diagnosis of B12 deficiency cannot be solely based on total serum B12 levels. Further testing of folic acid, intrinsic factor blocking antibodies (IFA), holotranscobalamin, homocysteine, and/or methyl malonic acid is suggested for symptomatic patients with haematological or neurological abnormalities.

• Haemolysed samples are not suitable for analysis. 

• Heterophilic antibodies and rheumatoid factor (RF) in human serum can react with reagent immunoglobulins, interfering with in vitro immunoassays. Patients routinely exposed to animals or to animal serum products can be prone to this interference, and anomalous values may be observed. Additional information may be required for diagnosis.

Related links

https://www.hse.ie/eng/about/who/cspd/lsr/resources/guideline-6-laboratory-testing-for-vitamin-b12-deficiency.pdf

Vitamin B12 is found in animal products such as meat, seafood, dairy products and eggs. Dietary deficiency of Vitamin B12 is unusual except in strict vegans. Causes of Vitamin B12 deficiency include pernicious anaemia, gastric resection and malabsorption. Pregnancy and long-term use of Metformin or proton pump inhibitor / H2 receptor antagonist may also lead to low Vitamin B12 levels. Vitamin B12 deficiency may lead to megaloblastic anaemia and neurological symptoms including peripheral neuropathy, cognitive impairment and sub-acute combined degeneration of the cord.

Indications for testing

• Haematological

– unexplained anaemia / other cytopenias

– unexplained macrocytosis

• Neurological

– sub acute combined degeneration of the cord

– peripheral neuropathy

– dementia

– unexplained neurology

• glossitis
• pregnancy
• malabsorption
• strict vegans
• previous gastric resection
• metformin therapy
• prolonged proton pump inhibitor or H2 receptor antagonist therapy

Note: There is no value in re-testing Vitamin B12 in patients who are already on parenteral Vitamin B12 unless FBC parameters or neurological symptoms fail to improve. Routine screening for Vitamin B12 deficiency is not indicated.

How to test

A Vitamin B12 immunoassay is currently the standard routine diagnostic test. It is a widely available and low cost test. However, it lacks specificity and sensitivity. The significance of Vitamin B12 test results should be assessed in conjunction with the clinical features. If there is strong clinical suspicion of Vitamin B12 deficiency despite a normal or borderline Vitamin B12 test result, treatment should not be delayed to avoid neurological impairment.

Additionally interpretation of the results can be difficult during pregnancy (active B12 recommended) and in patients on combined oral contraceptives.

Second line tests to help assess Vitamin B12 status include homocysteine, methylmalonic acid and holotranscobalamin, however these are not as widely available as the Total Vitamin B12 immunoassay at present.

Reference range

New normal reference range:

211-760 ng/l

Last updated

Fri, 23 Jan 2026 08:29:05 GMT