Unit Converter
Vitamin B6 (Pyridoxal Phosphate)

SI UNITS (recommended)

CONVENTIONAL UNITS

(Essential Water-Soluble Vitamin - Required for Amino Acid Metabolism, Neurotransmitters, Hemoglobin Synthesis & One-Carbon Metabolism)

Synonyms

  • Vitamin B6
  • Pyridoxal phosphate (PLP) - active form
  • Pyridoxal
  • Pyridoxamine
  • Pyridoxine
  • PLP
  • PNP (Pyridoxine phosphate)
  • PMP (Pyridoxamine phosphate)

Units of Measurement

  • nmol/L
  • µg/L
  • µg/dL
  • µg/100 mL
  • µg%
  • ng/mL

Unit Conversions

Molecular Weight of PLP = 247.14 g/mol

nmol/L ↔ µg/L

1 nmol/L=0.247 µg/L1\ \text{nmol/L} = 0.247\ \text{µg/L}1 nmol/L=0.247 µg/L 1 µg/L=4.04 nmol/L1\ \text{µg/L} = 4.04\ \text{nmol/L}1 µg/L=4.04 nmol/L

µg/dL → µg/L

1 µg/dL=10 µg/L1\ \text{µg/dL} = 10\ \text{µg/L}1 µg/dL=10 µg/L

ng/mL → µg/L

1 ng/mL=1 µg/L1\ \text{ng/mL} = 1\ \text{µg/L}1 ng/mL=1 µg/L

µg/100 mL = µg% = µg/dL

Description

Vitamin B6 is a water-soluble vitamin existing in six interconvertible forms, but pyridoxal-5-phosphate (PLP) is the major biologically active coenzyme.

PLP is essential for:

  • Amino acid metabolism
  • Neurotransmitter synthesis (GABA, dopamine, serotonin)
  • Hemoglobin synthesis & function
  • Gluconeogenesis
  • Immune function
  • One-carbon metabolism (with B12 & folate)

B6 must be obtained from diet; deficiency is common in malnutrition, alcoholism, dialysis, and drug therapy.

Physiological Role

1. Amino Acid Metabolism

PLP acts as a coenzyme in:

  • Transamination
  • Decarboxylation
  • Racemization
  • Deamination

2. Neurotransmitter Synthesis

PLP required for formation of:

  • Serotonin (from tryptophan)
  • Dopamine
  • Norepinephrine
  • GABA

3. Hematology

PLP is essential for heme synthesis → deficiency causes:

  • Microcytic anemia
  • Hypochromia

4. Homocysteine Metabolism

Low B6 → ↑ homocysteine
(PLP is cofactor for cystathionine-β-synthase)

5. Gluconeogenesis

PLP required for glycogen phosphorylase.

Clinical Significance

LOW VITAMIN B6

Common and clinically important.

Symptoms

  • Peripheral neuropathy
  • Seizures (especially infants)
  • Dermatitis, glossitis, stomatitis
  • Depression, irritability
  • Microcytic anemia (sideroblastic)
  • Increased homocysteine

Causes

  • Malnutrition
  • Alcohol use disorder
  • Chronic kidney disease / dialysis (high losses)
  • Malabsorption
  • Liver disease
  • Elderly
  • Pregnancy (increased demand)
  • Drugs:
    • Isoniazid (INH)
    • Hydralazine
    • Cycloserine
    • Penicillamine
    • Oral contraceptives

EXCESS VITAMIN B6

Usually from megadose supplements.

Symptoms

  • Sensory neuropathy (stocking-glove)
  • Gait disturbance
  • Photosensitivity
  • Nausea

Food sources do NOT cause toxicity.

Reference Intervals

(Tietz 8E, Mayo, ARUP, NIH)

Serum Pyridoxal-5-Phosphate

  • 20 – 125 nmol/L
     (= 5 – 31 µg/L)
    (= 5 – 31 ng/mL)

Deficiency

  • <20 nmol/L

Risk of neurologic symptoms

  • Often at <10 nmol/L

Diagnostic Uses

1. Suspected B6 Deficiency

Particularly in:

  • Dialysis patients
  • Alcoholics
  • Malabsorption
  • Isoniazid therapy
  • Elderly

2. Seizures in Infants

Pyridoxine-dependent seizures.

3. Peripheral Neuropathy Evaluation

Both deficiency and toxicity cause neuropathy.

4. Homocysteine Elevation

Part of B6–B12–folate panel.

5. Monitoring Supplementation

Especially in patients on high-dose or B6-containing regimens.

Analytical Notes

  • Use PLP measurement (most reliable form).
  • Fasting sample recommended.
  • Protect specimen from light (PLP is light-sensitive).
  • EDTA or heparin plasma commonly used.
  • LC-MS/MS is gold standard.

Clinical Pearls

  • Isoniazid therapy MUST be paired with B6 supplementation.
  • Both deficiency and toxicity can cause neuropathy, so clinical correlation is vital.
  • PLP falls quickly with inflammation, CKD, and alcoholism.
  • Pregnancy increases requirements; mild deficiency is common.
  • Low B6 with high homocysteine → risk for cardiovascular disease.

Interesting Fact

Vitamin B6 is involved in over 140 enzymatic reactions, making it one of the most metabolically active vitamins in human physiology.

References

  1. Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Vitamins
  2. NIH Office of Dietary Supplements - Vitamin B6
  3. WHO Micronutrient Guidelines
  4. Mayo Clinic Laboratories - PLP Test
  5. ARUP Consult - Vitamin Metabolism
  6. MedlinePlus (NIH) - Vitamin B6 Testing

Last updated: January 27, 2026

Reviewed by : Medical Review Board

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