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Blood Test Tracker

Vitamin B6 (Pyridoxal 5-Phosphate)

Measures pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, to see how much B6 your body has available.

AI-verified against cited sources. Awaiting expert reviewAlso called PLP, P5P, B6LOINC 30552-4

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What it is

Vitamin B6 helps your body use protein, make brain chemicals and build red blood cells. PLP is the active form that does this work. You get B6 from foods such as poultry, fish, potatoes, chickpeas and bananas, and from supplements and fortified foods. A fasting sample reflects your B6 status best, while a sample taken after a dose mostly shows what you just took in.

Why it matters

Low B6 can cause skin changes, a sore mouth or tongue, anemia and, in more serious cases, nerve problems. Very high B6 from long-term, high-dose supplements has been linked to nerve damage, with numbness or tingling in the hands and feet. The test is often ordered for unexplained nerve symptoms, when someone takes B6 supplements, or to look into a rare bone condition called hypophosphatasia, which can raise PLP.

If it’s low

A low result can be a sign that you are not getting enough B6, or that your body is using or clearing it faster. PLP also drops during inflammation or illness, so a low value does not always mean your diet is lacking.

Common causes

  • Low intake or a very limited diet
  • Alcohol use
  • Inflammation or acute illness
  • Kidney problems or low albumin
  • Conditions that reduce absorption, such as celiac disease or Crohn's disease
  • Some medications (your pharmacist can tell you whether yours affect B6)

What can help

  • Talk with a clinician about the cause and whether a B6 supplement fits your situation, since too much can also cause harm
  • Include B6-rich foods such as poultry, fish, potatoes, chickpeas and fortified cereals
  • Ask whether inflammation could be lowering your result and whether a CRP test would help

If it’s high

A high result most often means you took a B6 supplement or multivitamin recently. Sometimes a high PLP has another cause, such as a rare inherited bone condition called hypophosphatasia, where an enzyme that clears PLP from the blood is low. Long-term use of high-dose B6 supplements has been linked to nerve problems, so a high result is worth discussing if you take them.

Common causes

  • B6 or B-complex supplements, multivitamins and some energy drinks or fortified products
  • Hypophosphatasia (rare, with low alkaline phosphatase activity)

What can help

  • Review the B6 content of your supplements and multivitamin with a clinician or pharmacist
  • Ask whether an alkaline phosphatase test is worth checking if you don't take B6 supplements

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 5–50 ng/mL. Source: Mayo Clinic Laboratories, ARUP Laboratories, Fullscript (listing Quest Diagnostics test data), Frontiers in Nutrition, Behavioural Neurology.

PLP cutoffs used in US national survey (NHANES) reports (below 20 nmol/L from Institute of Medicine 1998; below 30 nmol/L from da Silva 2012)

  • Deficiencybelow 20 nmol/L
  • Insufficiency20 to under 30 nmol/L
  • Above the insufficiency cutoff30 and above nmol/L

What can affect your result

  • Recent supplement or multivitamin use
  • Fasting: a fasting sample reflects status; a non-fasting sample reflects recent intake
  • Inflammation, kidney function, albumin and alkaline phosphatase activity
  • Age, sex and ethnicity: in one Chinese adult study, PLP was lower in men aged 50 and older
  • Light exposure and handling of the sample
  • A sample taken after eating or taking a supplement mostly reflects recent intake, not long-term status (ARUP).
  • Mayo Clinic Laboratories asks patients not to take multivitamins or vitamin supplements for 24 hours before the draw.
  • The sample must be protected from light and frozen; light exposure can change the result (ARUP rejects samples that were not protected from light).
  • Inflammation, kidney problems, low albumin and changes in alkaline phosphatase activity can change PLP independent of intake.

Morning, after an overnight fast. A non-fasting sample reflects recent intake; a fasting sample reflects longer-term status (ARUP). No fixed timeline is published.

When to talk to a clinician

Talk with a clinician soon about numbness, tingling or burning in your hands or feet, especially if you take supplements that contain B6. Get urgent care for sudden weakness, confusion or a seizure.

Questions you could ask

  • Do any of my medications affect vitamin B6?
  • Could my supplements or multivitamin explain this level?
  • Do I need any follow-up if I don't take B6 supplements?
  • Could illness or inflammation be lowering my result?
  • Should we recheck it with a fasting sample?

Questions people ask

Why do the ranges differ so much between labs?

Labs use different methods and different groups of healthy people to set their ranges. For example, Mayo Clinic Laboratories uses 5-50 ng/mL, while ARUP uses 20-125 nmol/L, which is about 4.9-30.9 ng/mL. Compare your result with the range printed on your own report.

How do I convert ng/mL to nmol/L?

Multiply ng/mL by 4.046. For example, 10 ng/mL is about 40 nmol/L. ng/mL is the same as mcg/L and ug/L.

Show the science and sources

Units

  • 1 ng/mL = 1 ng/mL
  • 1 ng/mL = 4.046 nmol/L

Open the Vitamin B6 unit converter

For clinicians and researchers

PLP is the main active coenzyme form of vitamin B6 and the usual direct biomarker, measured in plasma by LC-MS/MS (Mayo) or similar methods; 4-pyridoxic acid is the main catabolite and is reported with PLP in Mayo's B6 profile. The Institute of Medicine (1998) used plasma PLP above 20 nmol/L as an adequacy criterion, and NHANES reports use below 20 nmol/L for deficiency and below 30 nmol/L for insufficiency. PLP is sensitive to non-nutritional factors: inflammation, renal dysfunction, alkaline phosphatase activity (PLP correlates negatively with ALP), hypoalbuminemia, ethnicity and supplement use can shift it independent of intake. Elevated PLP is a clue to hypophosphatasia, and Mayo lists the test for separating hypophosphatasia from supplementation as a cause. Lab intervals differ: Mayo 5-50 mcg/L (about 20-202 nmol/L) and Quest 5.1-54.8 ng/mL (about 21-222 nmol/L) versus ARUP 20-125 nmol/L. ARUP states that PLP in a fasting specimen indicates B6 nutritional status, while a non-fasting specimen reflects recent intake.

LOINC 30552-4 (primary), 62236-5. Specimen: plasma.

Sources

  1. Vitamin B6 Profile (Pyridoxal 5-Phosphate and Pyridoxic Acid), Plasma - Test ID B6PRO (Mayo Clinic Laboratories Extended Catalog), Mayo Clinic Laboratories
  2. Vitamin B6 (Pyridoxal 5-Phosphate) (test 0080111), ARUP Laboratories
  3. The Prevalence of Nutritional Imbalances in the US Population Over Time: Biomarker Data from the Cross-Sectional National Health and Nutrition Examination Survey (NHANES 1999-2000 through August 2021-August 2023), Current Developments in Nutrition (2026)
  4. Age- and sex-specific reference intervals and determinants of plasma vitamin B6 metabolites in healthy Chinese adults, Frontiers in Nutrition (2026)
  5. Toxic Effects of Excess Vitamins A, B6, and Folic Acid on the Nervous System, Behavioural Neurology (2025)
  6. Vitamin B6, Plasma (Quest Diagnostics test, adult interval as listed by Fullscript), Fullscript (listing Quest Diagnostics test data)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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