Vitamin B6 (Pyridoxine): What Your Test Shows

What is vitamin B6

Vitamin B6, also known as pyridoxine or pyridoxal-5-phosphate (PLP — the active form), is a water-soluble vitamin involved in more than 100 enzymatic reactions in the body. It is particularly important for amino acid metabolism, neurotransmitter synthesis (serotonin, dopamine, GABA), and immune function.

Vitamin B6 is obtained from food: poultry, fish, potatoes, bananas, chickpeas, nuts, and whole-grain products. In blood tests, pyridoxal-5-phosphate (PLP) in plasma is measured — it is the most accurate indicator of B6 status.

Reference ranges

The standard reference range for vitamin B6 (PLP) in blood is 20–125 nmol/L. As always, compare your result with the specific ranges provided by your laboratory.

A value below 20 nmol/L indicates deficiency. Above 125 nmol/L may indicate excess, most commonly associated with supplement use.

Why vitamin B6 may be elevated

Elevated vitamin B6 levels are almost always related to supplement use. Although B6 is water-soluble, long-term use of high doses (>100 mg/day) can cause sensory neuropathy — numbness and tingling in the hands and feet.

Very high PLP levels can also be seen with multivitamin preparations containing high amounts of B6. It is important to know that certain medications may increase PLP levels.

Why vitamin B6 may be low

B6 deficiency can occur due to inadequate nutrition, especially in older adults, vegetarians, and vegans with restricted diets.

Other causes include alcohol consumption (which disrupts B6 metabolism), certain medications — isoniazid (tuberculosis treatment), penicillamine, cycloserine, and oral contraceptives may lower B6 levels.

Chronic intestinal diseases (celiac disease, Crohn's disease) can impair B6 absorption. Kidney diseases, especially hemodialysis, also increase B6 loss.

B6 deficiency may manifest as: fatigue, irritability, depression, peripheral neuropathy, anemia (microcytic), skin rashes around the mouth, and impaired immunity.

What to do next

If your vitamin B6 level is low, discuss it with your doctor. Most commonly, a review of diet and medications is recommended. Food sources: poultry, salmon, potatoes, bananas, chickpeas.

If the level is high and you are taking supplements — it is important to review the dose. Long-term excess can cause nerve damage, which is usually reversible upon discontinuing excessive intake.

Your doctor may recommend checking other B6-related markers: homocysteine (B6 deficiency increases homocysteine), B12, and folic acid.

Tracking over time

Vitamin B6 is not routinely tested — it is usually checked when neurological symptoms, anemia, elevated homocysteine are present, or when taking medications that may lower B6.

If a deficiency is identified, a repeat test after 1–2 months allows assessment of whether the correction is effective. Alongside it, useful markers include: homocysteine, B12, folic acid, and a complete blood count.

Questions for your doctor

1. Does my B6 level indicate a clinically significant deficiency or excess? 2. Could my medications be affecting my B6 level? 3. Should homocysteine be checked? 4. If I am taking supplements — what dose is safe for long-term use? 5. Could my symptoms be related to my B6 status?