Vitamin B6 (PLP) Blood Test

Vitamin B6 includes several related compounds. PLP is an active coenzyme form and the most commonly used blood marker of B6 status. Pyridoxine on a supplement label is not the same measurement as plasma PLP on a test report.^{See reference 1}

Some laboratory profiles also measure pyridoxic acid, a B6-related breakdown product. Read the full analyte name rather than assuming every result labeled B6 can be compared directly.^{See reference 2}

Micrograms per litre (µg/L) and nanograms per millilitre (ng/mL) have equal numerical values: 10 µg/L equals 10 ng/mL. Nanomoles per litre describe a different quantity. Conversion requires the identity of the measured compound; do not reuse a factor for a different B6 form.^{See reference 1,See reference 6}

Keep the specimen, method, unit and laboratory interval attached to the number. A changed unit or assay can make two reports look different even before health changes are considered.^{See reference 5}

Mayo’s profile uses a 12-hour fast and asks that vitamin supplements be avoided for 24 hours before collection; its ranges were established under those conditions. Follow your own laboratory’s instructions and check any proposed interruption of prescribed treatment with the prescriber.^{See reference 2}

Bring the labels of multivitamins, B-complex products, magnesium or zinc supplements and other combination products. B6 may be present in more than one of them even when it is not prominent on the front label.^{See reference 3}

Low B6 status can occur with reduced intake, kidney disease, malabsorption, alcohol dependence and some medicines. Isolated deficiency is uncommon and can coexist with other nutrient deficiencies. The result does not identify which cause applies to you.^{See reference 1}

Testing can help investigate suspected deficiency, but symptoms and other findings still matter. A clinician can decide whether collection conditions, diet, medicines or another condition warrant further assessment.^{See reference 4,See reference 5}

Supplements or a nonfasting sample can increase PLP. Less commonly, persistently raised PLP can have another explanation, including hypophosphatasia; that assessment requires additional laboratory and clinical information.^{See reference 2}

Excess supplemental B6 can cause peripheral neuropathy, meaning damage to nerves outside the brain and spinal cord. Reported symptoms include tingling, burning or numbness. Australian safety reports include people taking multiple B6-containing products and amounts below previously assumed high-dose levels.^{See reference 3}

A laboratory upper limit and a supplement dose limit describe different things. Neither provides a personal guarantee of safety, and this guide does not define a PLP concentration that proves or excludes nerve injury.^{See reference 1,See reference 2,See reference 3}

If tingling, burning or numbness develops while using a B6-containing supplement, follow the product’s safety warning and seek medical advice promptly. The TGA advises stopping the implicated supplement and consulting a health professional. Prescribed medicines require a separate discussion with the prescriber.^{See reference 3}

Do not add another B6 product to treat unexplained nerve symptoms. A useful review includes when symptoms began, each product’s B6 amount, how long it was used, and the timing of the blood sample.^{See reference 1,See reference 3}