Vitamin B12 Investigations

Challenges in diagnosis

The diagnostic landscape for B12 deficiency is complex, notably due to the absence of a single, definitive diagnostic gold standard. This requires the careful integration of the patient's clinical presentation with the interpretation of various biochemical markers. The primary biomarkers traditionally employed are total serum vitamin B12 and holotranscobalamin (also known as Active B12), which represents the metabolically active fraction of B12 bound to its transport protein. Although Active B12 often offers better sensitivity and earlier detection of deficiency compared to total B12, it is a much more expensive test.

MBS revisions and implications

The recent revision to the Medicare Benefits Schedule (MBS) has introduced changes to the reimbursement structure for investigations related to vitamin B12 metabolism. Previously, the schedule promoted Active B12 levels for confirming low or borderline results. Under the revised schedule, while the option to test either total B12 or holotranscobalamin exists, the reimbursement provided by Medicare is now aligned with the lower cost of a total B12 assay. This adjustment presents a significant challenge for laboratories’ ability to offer Active B12 testing.

Ongoing availability of Active B12 testing

Australian Clinical Labs will continue to perform Active B12 tests but patients may have an out-of-pocket cost if they do not meet the criteria for a rebate. An outline of the new diagnostic pathway is shown below.

New diagnostic pathway for B12 testing

Inclusion of second-line biomarkers

The updated MBS acknowledges the multi-faceted nature of B12 deficiency diagnosis by including reimbursement for alternative, albeit indirect, biomarkers. Specifically, the schedule now provides for the testing of homocysteine (HCY) and methylmalonic acid (MMA) levels in the context of B12 deficiency investigation. Elevations in these metabolites can provide supplementary evidence supporting a diagnosis of B12 deficiency, particularly in cases where total B12 levels are equivocal or discordant with the clinical picture.

Clinical Labs’ testing strategy

Our laboratory is equipped to measure homocysteine levels and will proactively offer this analysis when the initial total B12 result falls within the deficient or potentially deficient range. This sequential testing strategy aims to provide clinicians with additional diagnostic information to guide their management decisions effectively and efficiently within the revised reimbursement structure.

Clinical vigilance remains key

We encourage clinicians to remain vigilant in their clinical assessment of patients at risk for B12 deficiency. Integrating the clinical context with the results of total B12, and where indicated, considering second-line tests such as HCY and potentially MMA, will be crucial in navigating the updated Medicare landscape while ensuring optimal patient care.

The major risk factors and clinical features of B12 deficiency are listed below.

Risk factors for B12 deficiency

• Restricted diet (veganism, vegetarianism)
• Autoimmune gastritis
• Family history of B12 deficiency
• Intestinal diseases (e.g. coeliac)
• Infections & surgical interventions
• Pregnancy & neonates
• Pharmaceutical interactions
• Nitrous oxide abuse
• Age greater than 65 years

Signs and symptoms of B12 deficiency

• Anaemia (weakness, tiredness, dyspnoea on exertion)
• Gastrointestinal (loss of appetite, sore tongue and mouth, epigastric discomfort, nausea, vomiting, heartburn)
• Neurological (numbness, pins and needles, impaired fine finger movements)
• Developmental delay in infants
• Positive Romberg’s sign
• Impaired vibration or position sense, impaired vision
• Orthostatic dizziness
• Loss of taste or smell
• Psychological & psychiatric disturbance

When to test for B12 deficiency

If a patient has at least 1 risk factor and 1 or more signs, then B12 assessment is warranted. It is also warranted if there are 1 or more signs or symptoms even with no risk factors if the clinician is concerned.

Interpretation of B12 results

OR

Next steps after diagnosis

If B12 deficiency is diagnosed, then the cause should be established. If the total B12 or Active B12 is abnormal or inconclusive, then the doctor should review the results alongside the clinical picture to determine if treatment is warranted. B12 deficiency is commonly corrected with oral or intramuscular doses of the vitamin, depending on the extent of symptoms, signs and levels of B12.

Considerations in pregnancy

During pregnancy, there are changes in the level of binding proteins which can cause a low total B12 level. In this situation, the Active B12 test is a more useful first line-test.

Updated MBS Items for B12 Testing from 1 July 2025

Amended Items

66838: Quantification of either or both of total vitamin B12 and holotranscobalamin. Applicable not more than once in 11 months.

66839: Quantification of methylmalonic acid or homocysteine, rendered in the same patient episode as a service to which item 66838 applies, if the result of that service is inconclusive or abnormal. Applicable not more than once in 11 months.

New Items

66842: Quantification of one or more of total vitamin B12, holotranscobalamin, methylmalonic acid or homocysteine for a patient:

(a) who:

• (i) is still experiencing symptoms of vitamin B12 deficiency 3 to 6 months after a service described in item 66838 or66839 was rendered for the patient; or
• (ii) obtained inconclusive results from a service described in item 66839; or

(b) to whom one or more of the following applies:

• (i) the patient has a diet low in vitamin B12;
• (ii) the patient has a family history of vitamin B12 deficiency or an autoimmune condition;
• (iii) the patient has previously had abdominal or pelvic radiotherapy; 
• (iv) the patient has previously had surgery involving the gastrointestinal tract;
• (v) the patient uses, or has a recent history of using, recreational nitrous oxide;
• (vi) the patient requires monitoring of vitamin B12 treatment;
• (vii) the patient uses vitamin B12‑antagonistic medicines;
• (viii) the patient has one or more clinical conditions with a recognised risk of vitamin B12 deficiency

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