Why B12 and Folate Are Tested Together
Vitamin B12 (cobalamin) and folate (vitamin B9) are tested as a pair because they share the same job and cause the same problems when deficient. Both are essential for DNA synthesis in fast-dividing cells — including the bone marrow cells that produce red blood cells — so deficiency in either one produces a characteristic macrocytic anaemia: low haemoglobin with abnormally large red cells (high MCV on a full blood count).
The catch is that the two have a dangerous interaction. Folic acid supplementation alone, in a B12-deficient patient, will fix the anaemia but allow the underlying B12-related neurological damage to silently progress. That is why both must always be tested together before treatment is started.
Australian Reference Ranges
| Test | Range | Notes |
|---|---|---|
| Serum B12 (total) | 200–700 pmol/L | Deficient below 200; borderline grey zone 200–300 where active B12 helps |
| Active B12 (holoTC) | ≥35 pmol/L | The biologically available fraction — more sensitive marker |
| Methylmalonic acid (MMA) | <0.4 µmol/L | Rises in functional deficiency. Confirms deficiency when B12 is borderline |
| Serum folate | ≥10 nmol/L | Reflects past few days of intake — rises quickly with food |
| Red cell folate | ≥740 nmol/L | Reflects 3–4 months — preferred test for true deficiency |
| Homocysteine | <15 µmol/L | Rises in both B12 and folate deficiency. Useful when MMA is unavailable |
Who Is at Risk in Australia
B12 deficiency affects up to 15% of Australian adults over 60, and is dramatically under-diagnosed because early symptoms are non-specific. The highest-risk groups:
- Vegans and strict vegetarians. B12 is only naturally present in animal products. Without supplementation or fortified foods (some plant milks, nutritional yeast), deficiency develops within 2–5 years of starting a fully plant-based diet.
- Adults over 60. Stomach acid declines with age, impairing the cleavage of B12 from food. Up to 15% of older Australians develop atrophic gastritis-related B12 deficiency.
- Long-term metformin users. Metformin reduces B12 absorption in the terminal ileum. Around 30% of patients on metformin for over 4 years develop measurable B12 deficiency. The RACGP recommends checking B12 annually in this group.
- Long-term PPI users. Omeprazole, esomeprazole and pantoprazole all reduce stomach acid and impair B12 absorption — clinically significant after 2+ years of daily use.
- Post-bariatric-surgery patients. Gastric bypass, sleeve gastrectomy and other procedures permanently alter B12 absorption. Lifelong supplementation is standard.
- Pernicious anaemia. An autoimmune condition where the body destroys intrinsic factor (the protein needed for B12 absorption). Affects 1–2% of Australians over 60. Diagnosed with intrinsic factor and parietal cell antibodies.
- Coeliac disease, Crohn disease, severe diverticular disease — any condition affecting the terminal ileum.
Folate deficiency is now uncommon in Australia thanks to mandatory folic acid fortification of bread flour introduced in 2009. The remaining at-risk groups are pregnant women (higher requirement), heavy alcohol users, people with severe malabsorption, and patients on methotrexate or anticonvulsants (phenytoin, carbamazepine).
The Symptoms — Early to Late
B12 deficiency is famously silent in its early stages. Recognising the pattern helps catch it before neurological damage becomes permanent.
Early (first 3–12 months)
- Persistent fatigue out of proportion to sleep and activity
- Brain fog, difficulty concentrating, mild memory issues
- Low mood, irritability
- Reduced exercise tolerance
- Glossitis — sore, smooth, red tongue
- Mouth ulcers, occasionally angular cheilitis
Mid-stage (6–24 months)
- Macrocytic anaemia appears on the FBC: haemoglobin starts to fall, MCV rises above 100 fL
- Mild peripheral pins-and-needles, especially in the feet
- Loss of normal vibration and proprioception sense
- Pale skin, palpitations on exertion
Late (untreated for many months)
- Subacute combined degeneration of the spinal cord — progressive numbness, weakness, gait instability
- Optic neuropathy and visual changes
- Cognitive impairment that can mimic early dementia
- Several of these neurological features can become permanent once they have been present for 6+ months
Folate deficiency rarely causes the neurological symptoms — it predominantly causes anaemia, fatigue, glossitis and (in pregnancy) neural tube defects in the developing fetus.
The Modern Australian Diagnostic Pathway
If your GP suspects deficiency, the standard workup is:
- Full blood count + serum B12 + serum folate as the first-line panel.
- If serum B12 is below 200 pmol/L and you have symptoms — that is enough to start treatment.
- If serum B12 is in the grey zone (200–300 pmol/L) but symptoms persist, request active B12 (holoTC) or MMA. MMA is the gold standard but is not on the standard MBS schedule.
- For confirmed deficiency, identify the cause: intrinsic factor antibodies and parietal cell antibodies (to test for pernicious anaemia), review medications (metformin, PPIs), dietary history, and gastrointestinal symptoms suggestive of coeliac or Crohn disease.
- If folate is low, also screen for coeliac disease (anti-tissue transglutaminase IgA + total IgA) — chronic folate deficiency in an Australian adult is unusual and warrants finding the cause.
Treatment in Australia
B12 — dietary deficiency
Oral cyanocobalamin 1000 µg daily for 3 months, then 250–500 µg daily long-term. Available over the counter in Australian pharmacies and supermarkets. Sublingual and buccal forms have no clinical advantage over standard oral tablets at equivalent doses.
B12 — absorption issues (pernicious anaemia, post-gastric surgery)
Hydroxocobalamin (Neo-B12) 1000 µg intramuscular injection. The standard PBS regimen: every other day for 1–2 weeks, then weekly until full blood count normalises, then maintenance every 3 months for life. Most Australian GPs administer the injections; some Australian pharmacies now offer them too. PBS-funded under streamlined authority for confirmed pernicious anaemia and post-gastric-surgery patients.
Folate
Oral folic acid 5 mg daily for 1–4 months is the standard PBS treatment. Recheck red cell folate after 3 months. Critical: never start folic acid for unexplained macrocytic anaemia until B12 has been measured — folic acid alone in a B12-deficient patient can mask the anaemia while neurological damage progresses.
Pre-conception folic acid
Folic acid 0.4–0.5 mg daily is recommended for all women planning pregnancy, starting at least 1 month before conception and continuing for the first 12 weeks. For women with previous neural tube defect history or on anticonvulsants, the dose is higher (5 mg daily). This is independent of any deficiency state.
What Affects B12 and Folate Accuracy
- Recent oral B12 supplements can falsely raise serum B12 for several weeks. If your GP wants a true baseline, stop supplements 1–2 weeks before testing.
- Recent folate intake rises serum folate within hours. Red cell folate is the more reliable measure.
- Pregnancy increases folate requirements significantly; reference ranges are higher.
- Certain medications elevate B12 falsely (oral contraceptives, some anticonvulsants).
- Liver disease can elevate serum B12 (it is stored in the liver).
Tracking B12 and Folate Over Time
For at-risk groups (vegans, long-term metformin/PPI users, post-bariatric-surgery patients), annual testing is recommended. After a deficiency has been treated, retest at 3 months to confirm response, then annually as part of routine monitoring. Most Australian pathology portals only show the past 1–2 results — uploading every report to BloodTrack reveals the multi-year trend, side by side with the related markers (full blood count, MCV, ferritin, homocysteine) that all move together when B12 status changes.
Bottom Line
B12 and folate are simple to test and simple to treat — but easy to miss because early symptoms are non-specific. If you are over 60, vegan, on metformin or a PPI long-term, post-bariatric, or have unexplained fatigue and brain fog, ask your GP for a B12 + folate + FBC. Always test both before treating either, and never start folic acid without a B12 result first.