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Vitamin B6 Test Explained

Vitamin B6 is essential for nerve function, red blood cell formation, and metabolism. Deficiency is uncommon but has serious neurological consequences if missed.

Written and clinically reviewed by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last reviewed and updated: · How we check our content

Normal range
20–125 nmol/L
Deficiency symptoms
Neuropathy, anaemia, dermatitis
Common causes
Alcohol excess, certain medications
Toxicity risk
With very high-dose supplements

Why B6 Matters

Vitamin B6 (pyridoxine) is a cofactor for over 100 enzyme reactions, particularly in amino acid metabolism, neurotransmitter synthesis, and haemoglobin production.

Causes of Deficiency

  • Chronic alcohol excess (most common cause in developed countries)
  • Certain medications: isoniazid (TB treatment), some anti-epileptics, penicillamine
  • Malabsorption conditions (coeliac disease, IBD)
  • Kidney disease (increased losses)
  • Poor dietary intake (rare in developed countries)

Symptoms of Deficiency

SystemSymptoms
Nervous systemPeripheral neuropathy: numbness, tingling, burning in hands/feet
BloodMicrocytic anaemia (unusual: B6 deficiency can mimic iron deficiency)
SkinDermatitis, cracks at corners of mouth
MoodDepression, confusion (severe deficiency)
Very High-Dose Supplements Can Cause HarmIronically, excessive vitamin B6 supplementation (often from high-dose over-the-counter supplements, >200mg/day for prolonged periods) can cause peripheral neuropathy: the same symptom as deficiency. Stick to recommended doses unless medically supervised.
Isoniazid and B6Anyone taking isoniazid for tuberculosis treatment is routinely co-prescribed vitamin B6 to prevent medication-induced peripheral neuropathy: a well-established drug interaction.
What foods are rich in vitamin B6?
Poultry, fish, potatoes, chickpeas, bananas, and fortified cereals are good sources. Deficiency from diet alone is uncommon in developed countries with varied diets.
Can B6 deficiency cause anaemia?
Yes. B6 deficiency can cause a sideroblastic anaemia, which can look similar to iron deficiency anaemia on a blood film, so B6 should be considered if iron studies are normal.
Is B6 testing routine?
No, it's not part of standard blood panels: it's specifically requested when peripheral neuropathy, unexplained anaemia, or relevant risk factors (alcohol excess, certain medications) are present.
Vitamin B12 TestRelated B vitaminNumbness & TinglingNeuropathy symptomsAnaemiaTypes and causes

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

  1. Vitamin B6 (Pyridoxine). In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK557436
  2. Ueland PM, Ulvik A, Rios-Avila L, Midttun Ø, Gregory JF. Direct and functional biomarkers of vitamin B6 status. Annu Rev Nutr. 2015;35:33-70. doi:10.1146/annurev-nutr-071714-034330 · PMID 25974692

Related reading

Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.

Testing is less useful than the history

Plasma pyridoxal 5-phosphate is the usual measurement, but it is not a routine test and is not needed in most people asking about B6. Isolated B6 deficiency is uncommon in people eating a varied diet, because the vitamin is widely distributed in meat, fish, poultry, potatoes, bananas and fortified cereals. Where deficiency does occur it is usually part of a broader picture: alcohol dependence, malabsorption, dialysis, or treatment with specific drugs. In practice a careful history of diet, alcohol and medication identifies the at-risk person more reliably than a level does.

Drugs that deplete B6

  • Isoniazid, used for tuberculosis, where pyridoxine is routinely co-prescribed precisely to prevent neuropathy.
  • Penicillamine and hydralazine, which bind the vitamin directly.
  • Cycloserine, and long-term anticonvulsants in some people.
  • Chronic alcohol use, which impairs both intake and conversion to the active form.

Too much B6 causes the problem it is taken to treat

This is the most important practical point about B6 and the reason it deserves a page of its own. Excess pyridoxine, taken as a supplement over months, causes a sensory peripheral neuropathy with numbness, tingling and unsteadiness. People frequently take high-dose B6 for tingling in the hands, then attribute worsening symptoms to the original problem rather than the remedy, and continue. Toxicity has been described at doses well below those found in some high-strength supplements, and B6 is present in many combination products, so the total daily intake is easy to underestimate. The neuropathy usually improves after stopping, though recovery can take months and is not always complete.

Because of this, several regulators have set upper limits on the amount permitted in over-the-counter supplements. If you take a B6-containing supplement and have new sensory symptoms, the supplement label is one of the first things to check.