Vitamin B6 test: what the result means

Vitamin B6 (pyridoxal phosphate) is one of the eight kinds of B-group vitamins (the B complex), which together support metabolism, take part in making healthy blood cells and support the working of the nervous system. Per MedlinePlus, B6 specifically helps brain development during pregnancy and infancy. The vitamin is obtained from food — meat, fish, legumes, nuts, grains — and the body does not store it for a long time, so a deficiency can develop relatively quickly if the diet is inadequate or if digestive system diseases interfere with it. For the test, blood is taken from a vein, or a urine sample is examined. The amount of B6 in the blood may be tested together with other B-group vitamins (for example B12, folic acid) when a deficiency is suspected and signs appear in the skin, the mucous membranes or the nervous system. Per MedlinePlus, interpreting the result is complicated by the fact that a normal amount of B6 does not necessarily rule out the cause of the symptoms — additional tests may be needed.

• When signs appear in the skin and mucous membranes — itchy rashes, cracks at the corners of the mouth, scaly skin on the lips, a swollen tongue (MedlinePlus)
• When there is coeliac disease, Crohn's disease or another digestive tract disease that interferes with the absorption of nutrients (MedlinePlus)
• When there is an alcohol use disorder, or a strictly restrictive diet that does not contain enough foods of animal origin (MedlinePlus)
• After digestive tract operations, or when taking medicines that can interfere with the absorption of B6 (MedlinePlus)
• When there are nervous system signs (for example numbness of the limbs) in someone taking large amounts of B6 supplements — to assess whether this is causing an overdose (NHS)

The exact numeric interval depends on the laboratory's method and is given on your result sheet. No publicly verified numeric reference limits from MedlinePlus or NHS have been published for this marker — that is why we do not state a specific interval here, so as not to invent a number. See also how to read blood test results.

A raised amount of vitamin B6 can be linked with long-term use of supplements in large doses. Per NHS, taking large doses of B6 supplements over a long time can disturb sensation in the arms and legs (peripheral neuropathy). Safe supplement limits are given by NHS; taking them is worth discussing with your doctor.

Causes listed for a high result:

• Long-term use of food supplements containing large doses of B6 (NHS)
• Excesses of other B-group vitamins are sometimes linked with certain features of liver function (MedlinePlus)

Possible symptoms:

• Disturbed sensation in the arms and legs (peripheral neuropathy) when large doses are taken over a long time (NHS)

What is usually looked at after a high result:

• Which food supplements are being taken and at what dose — to discuss with your doctor (NHS)
• Whether there are nervous system signs, for example numbness of the limbs or changes in sensation
• Whether liver function markers need to be assessed alongside

A low vitamin B6 result (deficiency)

A lowered amount of vitamin B6 indicates a deficiency, which per MedlinePlus can be caused by digestive system diseases or a restrictive diet. The typical signs are itchy rashes, cracks at the corners of the mouth, scaly skin on the lips and a swollen tongue. Other B-group vitamins, assessed alongside, help to tell the cause apart.

Causes listed for a low result:

• Coeliac disease, Crohn's disease or another digestive tract disease that interferes with the absorption of nutrients (MedlinePlus)
• An alcohol use disorder (MedlinePlus)
• A strictly restrictive diet that does not contain enough foods of animal origin (MedlinePlus)
• A previous digestive tract operation, or certain medicines that interfere with absorption (MedlinePlus)

Possible symptoms:

• Itchy rashes
• Cracks at the corners of the mouth
• Scaly skin on the lips
• A swollen tongue

What is usually looked at after a low result:

• Diet, and conditions that interfere with absorption (coeliac disease, Crohn's disease) — worth checking at the same time
• Alcohol drinking habits
• Other B-group vitamin markers (B12, folic acid), so that it is clear whether the deficiency is broader
• Medicines being taken that could affect absorption