Vitamin B6 – laboratory test

Description

Why vitamin B6 is tested

The test measures pyridoxal phosphate (PLP), the active form of vitamin B6, which is a cofactor in more than 140 enzymatic reactions: amino acid metabolism, synthesis of haem and neurotransmitters (serotonin, dopamine, GABA), and homocysteine metabolism. Deficiency is rare with a normal diet, but occurs in people with kidney disease, alcoholism, malabsorption syndromes and those taking certain medicines. Excess intake from supplements, which damages peripheral nerves, is now a more common problem.

When to consider this test

• numbness and tingling in the hands and feet, and balance problems in someone taking B6 supplements (suspected excess),
• seborrhoeic dermatitis, cracks at the corners of the mouth, inflammation of the tongue, irritability, depression, microcytic anaemia with normal iron levels (suspected deficiency),
• raised homocysteine despite normal B12 and folic acid levels,
• treatment with isoniazid, penicillamine, hydralazine or levodopa, long-term use of oral contraception,
• chronic kidney disease, dialysis, alcoholism, coeliac disease, Crohn’s disease, following bariatric surgery,
• treatment-resistant seizures in infants (pyridoxine-dependent epilepsy), at a neurologist’s request.

How to prepare

• Fast for 12 hours; drink only water in the morning. Have the sample collected in the morning.
• Do not take vitamin supplements, including B-complex and multivitamins, for 24 hours before sample collection. A doctor will decide whether a longer break is needed if the aim is to assess stores without supplementation.
• Bring a list of your medicines; some of them lower PLP.
• The test is performed at selected laboratories; check collection point availability when ordering.

How to interpret your result

The result is reported in µg/l or nmol/l (1 µg/l PLP = 4,05 nmol/l). The range depends on the method; as a guide, Mayo Clinic Laboratories gives 5–50 µg/l for people who have fasted and are not taking supplements.

Symptoms of neuropathy alongside a high result and supplement use are an indication to stop taking B6 products immediately, including those marketed for “stress relief” and “immune support”, which often contain several tens of milligrams.

What to test alongside vitamin B6

For neuropathy: vitamin B12, glucose, TSH; for anaemia: full blood count, ferritin, folic acid; for raised homocysteine, the full set of B vitamins. Read more: Badania-Medyczne.pl.

Sources: ALAB laboratoria, Vitamin B6 test (HPLC method, PLP, symptoms of deficiency and excess, limited availability); Mayo Clinic Laboratories, Vitamin B6, Plasma (PLP range 5–50 µg/l, fasting for 12 h, no supplements for 24 h, protection from light, interpretation of high values). This information does not replace a medical consultation.