Pyridoxal 5'-phosphate (PLP) in serum/plasma by enzymatic method
This test measures the active form of vitamin B6 (pyridoxal 5'-phosphate) in your blood, which is essential for many important body functions.
["PLP helps your body produce neurotransmitters and metabolize amino acids."]
Key facts at a glance
- LOINC
- 26056-2
- Short code
- Vit B6 p 250 mg Vit B6 PO SerPl-sCnc
- Synonyms
- Vit B6 p 250 mg Vit B6 PO SerPl-sCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Does This Test Measure?
Pyridoxal 5'-phosphate (PLP) is the active, biologically active form of vitamin B6. Your body converts vitamin B6 into PLP to use for various processes, including nerve function, red blood cell production, and metabolism of certain amino acids. This test specifically assesses the concentration of PLP in your blood, which can reflect your overall vitamin B6 status and metabolic needs.
Why Might You Need This Test?
Doctors may order this test if you have symptoms of vitamin B6 deficiency (such as nerve problems, anemia, or unusual skin changes), if you have certain medical conditions that affect vitamin B6 metabolism, or if you are taking medications that may interfere with vitamin B6 absorption or use.
What Does a Low or High Level Mean?
Low levels of PLP may suggest vitamin B6 deficiency, which can lead to health issues like nerve damage, anemia, or weakened immune function. High levels might indicate overconsumption of vitamin B6 supplements or certain metabolic conditions. However, reference ranges can vary by lab and individual health status, so results should be interpreted by your healthcare provider.
Common Reasons for Testing
This test is often used to evaluate vitamin B6 status in patients with suspected deficiencies, those undergoing long-term vitamin B6 supplementation, or individuals with conditions like isoniazid-induced neuropathy (a side effect of certain medications). It can also help monitor patients with genetic disorders affecting vitamin metabolism.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
PLP is a critical cofactor for enzymes involved in amino acid metabolism, neurotransmitter synthesis (like serotonin and dopamine), and hemoglobin production. Deficiencies can impair these processes, leading to neurological symptoms, anemia, or other metabolic disturbances. While vitamin B6 deficiency is less common than deficiencies of other B vitamins, PLP testing is valuable for diagnosing specific metabolic or medication-related issues.
Short name
PLP (Serum/Plasma)
Frequently asked questions
What causes vitamin B6 deficiency?
How is this test different from measuring total vitamin B6?
Can I take vitamin B6 supplements without checking my levels?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy