Patient Guide
Understanding Vitamin B12
What a borderline result means, and the simple next steps
~1 in 20Australians over 50 have a confirmed B12 deficiency
2+ yearson some reflux medicines or metformin raises your risk
Mostborderline results are simple to sort with one more test
A borderline B12 is common — and very sortable. Many people get a borderline B12 result on a routine blood test. It's a useful clue, not a cause for alarm — most causes are common, and there's a clear next step to find out what yours means.
What might be behind a low or borderline B12?
Not enough in your diet
B12 comes only from animal foods — meat, fish, eggs and dairy. A fully plant-based diet needs a B12 supplement.
More likely if: you eat little or no animal food.
Trouble absorbing it
Even with a good diet, your gut needs to absorb B12 properly. This gets harder with age, or with some stomach and gut conditions.
More likely if: you're older, or have a gut condition.
Pernicious anaemia
An autoimmune condition where the body attacks the stomach cells needed to absorb B12. It can run in families and needs lifelong B12 treatment once confirmed.
More likely if: other autoimmune conditions run in your family.
Certain medicines or substances
Long-term metformin, and reflux medicines taken for 2 years or more, can reduce how much B12 your body absorbs. Recreational nitrous oxide ('laughing gas') use can also lower B12 quickly.
More likely if: you're on metformin or a long-term reflux tablet.
What does a "borderline" result mean? Total B12 results sit on a scale, and a level in the middle — neither clearly low nor clearly normal — is sometimes called indeterminate or equivocal. Rather than guess, your GP or the lab can run a follow-up test (active B12, or a marker called MMA) that shows more clearly whether your body has enough B12 where it counts. Medicare rules changed in 2025 so these tests are usually funded only once every 11 months unless your result was borderline or you're at higher risk — which is exactly why a follow-up test, rather than just repeating the same one, is often the next step.
Start here: simple things that help
1
Eat B12-rich foods
Meat, fish, eggs & dairy — or a supplement if you eat little of these
2
Look after your gut
Treat reflux or gut issues — they can affect how well you absorb B12
3
List your medicines
Note how long you've been on metformin or a reflux tablet
4
Don't self-megadose
High-dose supplements taken before testing can mask the result — check with your GP first
Tell your GP promptly if you have
- Numbness, tingling or pins-and-needles in hands or feet
- Problems with balance or unsteadiness on your feet
- Memory, concentration or mood changes
- A sore, smooth or red tongue
- Marked breathlessness or a racing heart
- Symptoms that are getting worse
What your GP can check & do
- A follow-up test — active B12 or MMA
- A test for pernicious anaemia if no other cause is found
- A full blood count to check for anaemia
- A review of your diet and any relevant medicines
- Folate & iron levels often travel with B12
- Treatment with B12 tablets or injections
Worth noting before your appointment: how long you've been feeling this way; your diet (meat, fish, eggs or dairy intake); any gut symptoms (reflux, bloating, bowel changes); medicines (metformin or a long-term reflux tablet); family history of autoimmune disease; any recreational nitrous oxide use.
A Prompt, Not an Alarm
A borderline B12 is a prompt to look closer — not a cause for alarm. Caught early, low B12 is very treatable, and most people feel the difference.
— Dr Regu
