Vitamin B6 (fingerstick)

Vitamin B6 is needed for breaking down and building amino acids, for making blood and for the functioning of nerves and the immune system. It is found in meat, fish, eggs, bread and grain products, potatoes, legumes, vegetables and dairy products. The liver converts the different forms into the active form pyridoxal phosphate, which is what the test usually measures. Unlike many other water-soluble vitamins, too much vitamin B6 over a long period can be harmful.

• Too much vitamin B6 from supplements or multivitamins, with a risk of nerve damage in the hands and feet (peripheral neuropathy)
• Vitamin B6 deficiency with malnutrition, excessive alcohol use, kidney failure or use of isoniazid (a medicine against tuberculosis)

With a raised value and nerve symptoms, the GP asks about all supplements and products containing vitamin B6, usually advises stopping them and checks whether the symptoms decrease; with persistent or severe symptoms, referral to a neurologist follows. The side effect can be reported to the Netherlands Pharmacovigilance Centre Lareb. With a low value, the GP looks for the cause, such as alcohol use, diet, kidney function or medicines.

A strongly raised value in someone who takes supplements fits too high an intake and matters mainly when there are nerve symptoms. Because Lareb also received reports at low doses, the supplement use weighs just as heavily as the result itself. In people without symptoms a result says little: a deficiency hardly ever occurs, and a raised value mainly reflects recent supplement use.

• A supplement or multivitamin in the days before the blood draw raises the value; the result then mainly reflects recent intake.
• Vitamin B6 breaks down in sunlight; the sample must be protected from light until it is measured, otherwise the value may come out too low.
• After stopping supplements the value drops, while nerve symptoms may persist.
• Reference values differ per laboratory.

According to the Netherlands Nutrition Centre (Voedingscentrum), a vitamin B6 deficiency hardly ever occurs in the Netherlands. Symptoms from too much vitamin B6 do occur: the Netherlands Pharmacovigilance Centre Lareb received 238 reports of nerve symptoms in people using products containing vitamin B6, 79 of them at a daily dose of 12 milligrams or less. How often a too-high value occurs in people who take supplements is not known.

Useful with tingling, numbness or pain in the hands or feet in someone who takes supplements, multivitamins or other products containing vitamin B6. Also useful when a deficiency is suspected in risk groups, such as with excessive alcohol use, malnutrition, kidney failure or use of isoniazid. In healthy people without symptoms the result adds little.

• A normal value can give false reassurance with nerve symptoms if someone stopped taking B6 supplements shortly before.
• A slightly raised value due to a multivitamin in someone without symptoms can cause unnecessary worry.

• NVKC, allesovertesten.nl: Vitamine B6
• Voedingscentrum: Vitamine B6
• Bijwerkingencentrum Lareb: Zenuwschade door gebruik van voedingssupplementen met vitamine B6