Overview
Quick answer
Vitamin B12 (cobalamin) is essential for making DNA and red blood cells, and for maintaining the protective myelin sheath around nerves. A blood test reports total B12 in pmol/L, and Australian guidance now reads it as three bands rather than one reference range: below 133 pmol/L is likely deficient, 133 to 258 pmol/L is indeterminate (a genuine grey zone, not a clean normal), and above 258 pmol/L is unlikely to be deficient.
When total B12 lands in that grey zone, Australian labs commonly add active B12 (holotranscobalamin), the fraction your cells can actually use: below 25 pmol/L likely deficient, 25 to 70 pmol/L indeterminate, above 70 pmol/L unlikely deficient. A functional marker, usually methylmalonic acid (MMA) or homocysteine, can settle a result that is still unclear.
B12 deficiency is not just a vegan issue. Long-term metformin use, long-term proton pump inhibitor or H2-blocker use, age 50 and over, pernicious anaemia, and gut conditions that affect absorption all raise real risk, several with a quantified effect size from published studies. And because Australia fortifies bread flour with folic acid, the anaemia that would normally flag B12 deficiency can be masked, so neurological symptoms sometimes appear first, with no anaemia clue on the full blood count.
Overview
Key takeaways
Total B12 is read as three bands, not one reference range: under 133 pmol/L likely deficient, 133 to 258 pmol/L indeterminate, over 258 pmol/L unlikely deficient, per the current Australian Prescriber guidance.
Active B12 (holotranscobalamin), the cell-available fraction, is the usual follow-up test when total B12 sits in the grey zone: under 25 pmol/L likely deficient, 25 to 70 pmol/L indeterminate, over 70 pmol/L unlikely deficient.
B12 deficiency in Australians aged 50 and over is estimated at 5.2% to 6.3%. There is no reliable published whole-population Australian deficiency rate, so treat any figure claiming otherwise with caution.
Long-term metformin use (more than 3 years) is linked to more than double the odds of biochemical B12 deficiency compared with shorter metformin use in a widely cited study; long-term proton pump inhibitor and H2-blocker use carry a smaller but real, separately quantified risk.
Nitrous oxide inactivates B12 at the molecular level. It can leave both total and active B12 looking normal on a blood test despite a real functional deficiency, which is why recent or repeated nitrous oxide exposure is worth mentioning to whoever orders your test.
Australia's mandatory folic acid fortification of bread flour can correct the anaemia that would normally flag B12 deficiency, so neurological symptoms, tingling, balance changes, memory problems, can appear with a completely normal full blood count.
There is no established upper safety limit for B12 because excess is excreted by the kidneys, and short-term high intake is not a concern. One large cohort study did find an association between very high, long-term supplemental B12 use and lung cancer risk in men, strongest in smokers, worth knowing but not a reason to avoid a normal test-driven correction.
Basics
What vitamin B12 does, and why deficiency is a two-system problem
Vitamin B12 is a water-soluble vitamin your body cannot make. Every molecule comes from diet or supplementation, and unlike most water-soluble vitamins, the liver stores several years' worth, which is part of why deficiency can take a long time to show up even after intake stops.
Two enzymes, two systems
B12 is a required cofactor for methionine synthase, which feeds DNA synthesis and myelin production through the folate cycle, and for methylmalonyl-CoA mutase, which handles the breakdown of certain fats and amino acids. When the second enzyme stalls from lack of B12, methylmalonic acid (MMA) builds up in blood, which is exactly why MMA is used as a functional marker of deficiency.
A long, deliberately inefficient absorption chain
Dietary B12 arrives bound to protein in food. Stomach acid and pepsin free it, gastric intrinsic factor (secreted by the stomach's parietal cells) binds it, and the intrinsic factor-B12 complex survives digestion intact until specialised receptors at the far end of the small intestine, the terminal ileum, absorb it. Almost every step in that chain, acid production, intrinsic factor, or the terminal ileum itself, is a separate point where something can go wrong, which is why the causes section below covers such a wide range of unrelated conditions and medications.
Only a fifth of your blood B12 is actually usable
Roughly 80% of circulating B12 is bound to a transport protein called haptocorrin, which is not available to your cells. The remaining fraction, bound to transcobalamin, is the biologically active portion, measured directly as active B12 (holotranscobalamin). That is the physiological reason a low-normal total B12 does not always mean a real problem, and why active B12 exists as a more targeted follow-up test rather than a fancier version of the same measurement.
That two-enzyme dependency is why B12 deficiency is really two overlapping problems rather than one: a blood problem (impaired DNA synthesis in bone marrow, producing abnormally large, immature red cells) and a nerve problem (a breakdown in myelin maintenance). Either can appear without the other, which is the root cause of most of the confusing, seemingly contradictory advice this guide untangles below.
Reading your results
How to read your vitamin B12 test report
An Australian B12 test result usually reports one or more of the following fields. Reading them as a set, rather than total B12 alone, is what separates a genuinely useful result from one that is easy to misread.
Vitamin B12 (total)
Reported in pmol/L, the standard Australian first-line test. It measures both the active (transcobalamin-bound) and inactive (haptocorrin-bound) fractions together, which is why a result in the grey zone does not automatically mean deficiency.
Active B12 (holotranscobalamin)
The cell-available fraction only, also in pmol/L. Used as first-line testing in pregnancy, or as a follow-up when total B12 is indeterminate. If you're comparing to an overseas result reported in pg/mL rather than pmol/L, pg/mL × 0.738 ≈ pmol/L (or pmol/L × 1.355 ≈ pg/mL), based on B12's molecular weight.
Methylmalonic acid (MMA)
A functional marker: it rises specifically when B12-dependent methylmalonyl-CoA mutase stalls, so it is not fooled by a borderline blood level the way total B12 can be. It is not part of a routine panel and is added selectively, MBS item 66842 covers it in defined circumstances rather than as a default add-on.
Homocysteine
Another functional marker, elevated by B12, folate or vitamin B6 deficiency (all feed the same remethylation pathway), so a raised result needs those vitamins checked before concluding which one is short. Also affected by kidney function, thyroid status and some medications, so it is a supporting clue rather than a standalone diagnosis. Unlike total B12, it is usually collected after an overnight fast.
Folate
B12's metabolic partner, reported in nmol/L. Tested alongside B12 partly because the two deficiencies produce an identical-looking blood picture (macrocytic, megaloblastic anaemia) and partly because, as the masked-anaemia section below explains, Australia's folate fortification can complicate the picture in the other direction.
| Test | Likely deficient | Indeterminate | Unlikely deficient |
|---|---|---|---|
| Total B12 (pmol/L) | Below 133 | 133 to 258 | Above 258 |
| Active B12 / holotranscobalamin (pmol/L) | Below 25 | 25 to 70 | Above 70 |
If total B12 comes back in the indeterminate band, that is not an ambiguous result to shrug off, it is the specific signal the current Australian guidance says should prompt an active B12, MMA or homocysteine follow-up rather than a wait-and-see approach.
Beyond the reference range
Reference range vs a preventative target
The interpretive bands above are diagnostic, built to identify a deficiency that already needs treatment. Hemexa's own preventative band is deliberately tighter, aimed at catching a downward trend well before a member reaches that point.
Hemexa flags optimal at 300 pmol/L or above, with a watch band from 150
Hemexa's own clinical policy treats total B12 at or above 300 pmol/L as the preventative optimal band, with a watch flag from 150 up to 300 pmol/L and an action flag below 150 pmol/L. This is Hemexa's working preventative policy, layered on Healius Pathology's reported reference range, not a claim that 150 to 300 pmol/L is itself a diagnosis; it sits above the diagnostic "likely deficient" cut-off of 133 pmol/L on purpose, so a member sees a flag before a level a GP would call frank deficiency.
The point of watching from 150 to 300 is trend, not verdict
A result of 220 pmol/L sits inside the indeterminate band, not the likely-deficient one, so it is not a diagnosis on its own. It is also not a clean normal. Current Australian guidance treats that grey zone as the reason to add active B12, MMA or homocysteine rather than wait, and a drop from last year's 340 is worth noticing because B12 stores can decline gradually for years, especially in a slowly progressing cause like a changing diet or a new long-term medication.
Discuss any watch-band result with your GP rather than treating it as a verdict on its own; the value of an annual baseline is the trend it builds, not any single year's number.
Why online B12 ranges disagree, and why a reference interval is not a clinical decision limit, is on the reference range vs optimal range guide.
A common source of confusion
Why the B12 range you see online may not agree with another one
If you search for a B12 reference range online, you will find several different numbers, and they are not all wrong, they are measuring against different standards. This is worth understanding before you compare your own result to something you found on a forum or a competitor's website.
Australian guidance has moved from a single range to three-tier bands
An older (1999) Australian Prescriber article quoted a single reference range, roughly 150 to 600 pmol/L. Current guidance, the 2026 Bedz and Forsyth Australian Prescriber article this guide is built on, has moved past a single range entirely, to the three-tier likely-deficient / indeterminate / unlikely-deficient bands used throughout this guide. A single range and a set of interpretive bands are answering different questions, and a page that only quotes an old single range is working from superseded guidance, not necessarily wrong guidance, just dated.
Every pathology lab sets its own reference interval
Reference intervals are also lab-specific, calculated from each laboratory's own instrument and local population, which is exactly why you will see mildly different numbers printed on results from different Australian pathology providers. This is normal and does not mean either lab is wrong; it means the number printed on your particular report should be read alongside the clinical interpretive bands above it, not compared directly to a number from a different provider's website.
Hemexa's own preventative watch band, described above, is a third and different thing again: not a diagnostic range at all, but a deliberately more conservative early-warning threshold layered on top of the diagnostic bands.
How common
How common is B12 deficiency in Australia?
5.2% to 6.3% of Australians aged 50 and over are deficient
The current Australian Prescriber article on B12 deficiency testing and treatment cites this as the figure for Australians aged 50 and over. There is no reliable published whole-population Australian deficiency rate, for any age, worth quoting alongside it, and this guide will not invent one.
The ABS collected B12 data nationally, but has not published it for the general population
The ABS National Health Measures Survey 2022-24, Australia's main biomedical population survey, did collect serum vitamin B12 as part of its blood panel. Its published results, however, cover vitamin D, folate, iron and several other markers, but not B12, for the general Australian population. B12 status in the general population is, right now, a genuine data gap rather than a known quantity.
The only published ABS B12 figures are for a different, specific population
The companion National Aboriginal and Torres Strait Islander Health Measures Survey 2022-24 did publish serum B12 results, but specifically for the Aboriginal and Torres Strait Islander population it surveyed: mean 398 pmol/L in males 18 and over, 371 pmol/L in females 18 and over, and 348 pmol/L in adults 55 and over, with 98.2% of females aged 16 to 44 at or above 150 pmol/L. These figures describe that specific population and should not be extrapolated to Australians generally.
Who should test
Who should consider a B12 test?
Diet and life stage
- A vegan or strict vegetarian diet, since B12 is essentially absent from unfortified plant foods
- Pregnancy or breastfeeding, particularly on a vegan or vegetarian diet
- Age 50 and over, when reduced stomach acid production becomes more common
Medications and procedures
- Metformin use of 3 years or more
- Long-term (2 years or more) proton pump inhibitor or H2-blocker use
- Previous bariatric or gastric surgery
- Recent or repeated nitrous oxide exposure, recreational or medical
Conditions and history
- Pernicious anaemia, or a family history of it
- Crohn's disease, coeliac disease, or another condition affecting the terminal ileum or small bowel absorption
- Persisting symptoms 3 to 6 months after a prior B12 test, or an inconclusive result
Australian guidance recommends B12 testing when there are symptoms or a recognised risk factor, not as general-population screening. A preventative annual panel that includes B12 is a different use case, usually private, and your GP can advise whether a defined MBS risk criterion applies to you.
Causes
What causes B12 deficiency
B12 deficiency has a genuinely wide set of causes, which is a direct consequence of how many separate steps its absorption pathway requires. None of these is diagnosed from a B12 level alone; each needs the wider clinical picture.
Pernicious anaemia
An autoimmune condition where the immune system attacks the stomach's acid- and intrinsic-factor-producing parietal cells, eventually leaving too little intrinsic factor to absorb B12 regardless of dietary intake. Intrinsic factor antibodies are considered close to diagnostic when present but are only detected in around half of actual cases, so a negative antibody test does not rule pernicious anaemia out.
Metformin
A widely cited 2006 case-control study of people already taking metformin found use exceeding 3 years associated with more than double the odds of biochemical B12 deficiency compared with shorter use (adjusted odds ratio 2.39), with each additional 1 g/day of dose independently raising the odds further (odds ratio 2.88 per gram). The proposed mechanism is interference with the calcium-dependent step in intrinsic-factor-B12 absorption at the terminal ileum, an effect reversed with oral calcium in a small 14-person study, not a reason to self-prescribe calcium or to stop metformin without medical advice.
Proton pump inhibitors and H2-blockers
A large case-control study found proton pump inhibitor use of 2 years or more associated with 65% higher odds of B12 deficiency (higher again, 95%, at higher doses), and H2-blocker use of 2 years or more with 25% higher odds. The mechanism is reduced stomach acid impairing the release of B12 from dietary protein, food-bound B12 malabsorption, which does not typically affect absorption of already-free B12 from a supplement or fortified food.
Nitrous oxide
Nitrous oxide oxidises the cobalt atom at B12's core, inactivating that B12 molecule so methionine synthase cannot use it, regardless of how much B12 is sitting in blood. Fresh B12 can restore the enzyme. Case reports describe this producing subacute combined degeneration, demyelination of the spinal cord's dorsal and lateral columns, causing loss of vibration sense, proprioception and gait control, sometimes after repeated recreational exposure in someone with no other obvious risk factor.
Gut conditions and surgery
Crohn's disease, coeliac disease and other conditions affecting the terminal ileum can physically prevent absorption regardless of intrinsic factor status, and bariatric or gastric surgery can remove or bypass the sections of the gut B12 absorption depends on.
Dietary deficiency, covered in the food sources section below, is the most common cause worldwide but is only one entry on a longer list; a low result in someone eating a varied omnivorous diet is a reason to look at the other causes above, not a reason to assume the test is wrong.
Symptoms
Signs and symptoms of B12 deficiency
B12 deficiency symptoms fall into distinct categories, and the confusing part for most people is that they do not all appear together, or in a predictable order.
Nonspecific
- Fatigue
- Weakness
- Stomatitis (mouth soreness or a sore, swollen tongue)
- Unintended weight loss
- Reduced appetite
Neurological
- Pins and needles or numbness (paraesthesia), typically in the hands and feet
- Peripheral neuropathy
- In more advanced or prolonged cases, subacute combined degeneration: loss of vibration sense, proprioception and balance
Psychiatric and cognitive
- Irritability
- Personality changes
- Memory impairment
- Depression
- In severe cases, delirium or psychosis
Blood
- Megaloblastic anaemia (abnormally large, immature red blood cells)
- Pancytopenia (a fall across all blood cell types) in more severe cases
Neurological and psychiatric symptoms can appear on their own, without anaemia, which is the same underlying point the masked-anaemia section below makes from a different angle: a normal full blood count does not clear B12 as a possibility if the history still points there.
A special case
The clue that can go missing: folate and masked anaemia
Why a completely normal full blood count does not rule out B12 deficiency
Australia has mandated folic acid fortification of bread-making wheat flour since September 2009. Folate and B12 feed the same enzyme step, so adequate folate can mask the megaloblastic anaemia that would otherwise be the clearest, earliest clue to B12 deficiency, correcting the blood picture while the separate, B12-specific neurological damage keeps progressing underneath a normal-looking blood count. This is why a persuasive history, tingling hands and feet, balance changes, unexplained memory or mood changes, deserves a B12 test even when a full blood count looks entirely unremarkable.
The other direction
Can vitamin B12 be too high?
Unlike fat-soluble vitamins, B12 does not build up to toxic levels in the way vitamin A or D can. It is water-soluble, and the kidneys excrete what the body does not use, which is the mechanism behind why no established upper safety limit exists for B12 from any authoritative body. A high number on a report is still worth reading in context.
An unexpectedly high result can be a clinical signal, not a toxicity finding
A high total B12 in someone who is not taking a high-dose supplement is not automatically harmless overflow. Australian guidance notes that raised haptocorrin in acute inflammation, myeloproliferative disorders or liver disease, and assay interference from intrinsic-factor antibodies, can push total B12 up and can even mask a tissue deficiency. That is a reason to read a high result against the rest of the clinical picture, not a reason to assume more B12 is always better.
One real, specific supplement caveat worth knowing, not a reason for alarm
A large US cohort study following supplement use over roughly a decade found long-term, high-dose supplemental B12 (an average intake above 55 micrograms a day) associated with a near-doubling of lung cancer risk in men, an association strongest among current male smokers. This is an observational association in long-term, high-dose supplement users, not a finding about a normal diet, a food-fortification level, or correcting a confirmed deficiency under medical guidance, and it has not been shown to be causal. It is a real, citable reason not to self-prescribe very high-dose B12 indefinitely without a reason, not a reason to avoid testing or treating a confirmed deficiency.
Food and supplementation
Food sources, and who needs a supplement
B12 is made by bacteria, not plants or animals, which is why it reaches your plate almost exclusively through animal products, or through foods deliberately fortified with it.
Animal sources
- Meat, especially liver
- Fish and shellfish
- Eggs
- Dairy products
Sources for a vegan or vegetarian diet
- Fortified plant milks
- Some fortified meat-substitute products
- Some fortified breakfast cereals
- A B12 supplement, which Healthdirect notes the Australian Dietary Guidelines advise for anyone eating a vegan diet
B12 is essentially absent from unfortified plant foods, which is the specific reason vegan and strict vegetarian diets carry a real, well-established deficiency risk that a varied omnivorous diet does not.
How to order
How Australians get a B12 test
| Approach | Best for | Typical cost | Includes test? |
|---|---|---|---|
| GP-ordered, Medicare-funded | Most people: symptoms, a known risk factor, or routine monitoring | Bulk-billed or low gap when eligible. Item 66838 (total and/or active B12) bills at schedule fee $23.60, no more than once in 11 months for most people | Yes, total B12 and/or active B12 |
| GP-ordered, Medicare-funded (expanded) | Persisting symptoms 3 to 6 months after a prior test, an inconclusive result, or a defined risk group | Item 66842 covers total B12, active B12, MMA and/or homocysteine, schedule fee $23.60, with no explicit frequency cap in the item wording itself | Yes, potentially including the functional markers MMA and homocysteine |
| GP-ordered, private (no clinical indication) | Preventative or asymptomatic testing outside MBS criteria | Varies by pathology provider; typically bundled within a broader private nutrient or preventative panel | Yes, as part of a broader panel |
| Membership platforms (e.g. Hemexa) | Ongoing annual baseline coverage with trend tracking alongside other nutrients | ~$1,199/year (full membership) | Yes; vitamin B12 and folate on the annual baseline, among 76–80 signature markers |
No fasting is required for total B12, active B12 or MMA. If homocysteine is added as a follow-up, an overnight fast is the usual collection instruction, because a recent protein meal can raise the result. Pathology in Australia requires an authorised request from a registered medical practitioner; mention any recent nitrous oxide exposure, long-term metformin, PPI or H2-blocker use, or a vegan or vegetarian diet, since these change how a borderline result should be read.
FAQ
Frequently asked questions
- What is a normal vitamin B12 level in Australia?
- Current Australian guidance reads total B12 as three bands rather than a single normal range: below 133 pmol/L is likely deficient, 133 to 258 pmol/L is indeterminate, and above 258 pmol/L is unlikely to reflect deficiency. If your result falls in the indeterminate band, an active B12, MMA or homocysteine follow-up is the usual next step, not a wait-and-see approach.
- What is the difference between total B12 and active B12?
- Total B12 measures all circulating B12, including the roughly 80% bound to haptocorrin, which is not available to your cells. Active B12 (holotranscobalamin) measures only the cell-available fraction. Active B12 is used first-line in pregnancy, and as a follow-up when total B12 sits in the indeterminate band.
- Can you have a normal B12 level and still be deficient?
- Yes, in more than one well-documented way. The common one is a total B12 in the indeterminate or low-normal band with a raised MMA or homocysteine, meaning the enzymes are already short even though the level has not crossed the likely-deficient cut-off. Pregnancy can also lower total B12 by reducing haptocorrin without a true tissue deficiency, which is why active B12 is first-line then. Nitrous oxide is the special case: it inactivates the B12 molecule itself, so both total and active B12 can look normal despite a real functional deficiency. That is why recent or repeated nitrous oxide exposure is worth mentioning, and why MMA or homocysteine can catch what a level alone misses.
- How common is B12 deficiency in Australia?
- The most recent Australian Prescriber article on the topic cites 5.2% to 6.3% of Australians aged 50 and over as deficient. There is no reliable published whole-population Australian rate; the ABS collected B12 data nationally in its 2022-24 survey but has published results only for the Aboriginal and Torres Strait Islander population it separately surveyed, not the general population.
- Does metformin cause B12 deficiency?
- It is a well-established risk factor, not a certainty. A widely cited case-control study of people already taking metformin found use exceeding 3 years associated with more than double the odds of biochemical B12 deficiency compared with shorter use, with each additional 1 g/day of dose independently raising the odds further. The likely mechanism is interference with calcium-dependent B12 absorption in the terminal ileum, an effect reversed with oral calcium in a small study. This is a reason for periodic testing on long-term metformin, not a reason to stop the medication or to self-prescribe calcium without medical advice.
- Can proton pump inhibitors (PPIs) cause B12 deficiency?
- Long-term use, generally 2 years or more, is associated with meaningfully higher odds of B12 deficiency in large studies (65% higher at standard doses, up to 95% higher at higher doses), because reduced stomach acid impairs release of B12 that is bound to protein in food. This effect does not typically extend to B12 from a supplement or fortified food, since that form is already free rather than protein-bound.
- What are the symptoms of B12 deficiency?
- They cluster into nonspecific symptoms (fatigue, weakness, a sore tongue, weight loss), neurological symptoms (tingling or numbness in the hands and feet, and in more advanced cases loss of balance and vibration sense), psychiatric and cognitive symptoms (irritability, memory problems, depression, and in severe cases delirium or psychosis), and blood changes (megaloblastic anaemia). These do not always appear together, and neurological or psychiatric symptoms can appear without anaemia.
- Can B12 deficiency cause anaemia without any other symptoms, or symptoms without anaemia?
- Both, and that inconsistency is a real feature of the condition worldwide, not a sign the test is unreliable. Neurological symptoms without anaemia are well documented even without fortification. Australia's mandatory folate fortification of bread flour can add a further reason the anaemia clue goes missing, while the separate neurological damage keeps progressing.
- Do I need to fast for a vitamin B12 test?
- Not for total B12, active B12 or MMA. Homocysteine, if it is added as a follow-up, is usually collected after an overnight fast (RCPA recommends 12 hours), because a recent protein meal can raise the result.
- Is it possible to take too much B12?
- There is no established upper safety limit for B12, because it is water-soluble and excess is excreted by the kidneys. An unexpectedly high blood result in someone not taking a high-dose supplement can still be a clinical signal, including liver disease, myeloproliferative disorders, or assay interference, and can even mask a tissue deficiency. One large long-term cohort study did find an association between very high-dose supplemental B12 use over about a decade and increased lung cancer risk in men, strongest among smokers; this is a caveat for indefinite very high-dose supplementation without a reason, not a finding about correcting a confirmed deficiency or normal food-fortification levels.
- Are vegans and vegetarians the only people at risk of B12 deficiency?
- No. Diet is one of several well-established risk factors, alongside long-term metformin use, long-term PPI or H2-blocker use, age 50 and over, pernicious anaemia, prior bariatric or gastric surgery, and gut conditions such as Crohn's disease or coeliac disease that affect absorption in the terminal ileum.
- How much does a B12 test cost in Australia, and does Medicare cover it?
- When clinically indicated, Medicare funds total and/or active B12 under MBS item 66838 (schedule fee $23.60), usually bulk-billed, limited to once every 11 months for most people. A broader item, 66842, covers additional markers including MMA and homocysteine for people with persisting symptoms, an inconclusive prior result, or a defined risk factor. Outside a clinical indication, cost varies by provider. Membership platforms that include B12 on a comprehensive annual baseline start around AU$1,199 per year.
How Hemexa fits
How Hemexa can help
B12 is easiest to read correctly as a trend across years, alongside folate and the rest of the full blood count, with a preventative band that flags a downward trajectory well before it reaches a diagnostic threshold.
Vitamin B12 and folate on the annual baseline
Hemexa includes vitamin B12 and folate on the 76–80 marker annual baseline, grouped in the nutrients category alongside vitamin D and zinc, so a year-on-year trend is visible rather than buried inside a single result.
A watch band from 150 pmol/L, ahead of the diagnostic threshold
Hemexa's dashboard shows your B12 result against both the standard reference range and a tighter preventative watch band starting at 150 pmol/L, up to an optimal floor of 300 pmol/L, so a result that is still technically fine but trending down is visible before it would prompt a diagnostic conversation.
Active B12 available when the picture needs it
Active B12 (holotranscobalamin) is available as an add-on for members whose total B12 sits in the indeterminate band or whose history warrants a more targeted result, the same follow-up pattern Australian guidance recommends.
Sources
References
Bedz, S., & Forsyth, C. (2026). Vitamin B12 deficiency: testing and treatment. Australian Prescriber, 49(2). View source ↗
Stabler, S. P. (2013). Vitamin B12 deficiency. New England Journal of Medicine, 368, 149-160. View source ↗
Medicare Benefits Schedule, Item 66838. View source ↗
Medicare Benefits Schedule, Item 66842. View source ↗
Australian Bureau of Statistics. National Health Measures Survey, 2022-24 (biomedical collections methodology, confirming serum vitamin B12 collection). View source ↗