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Pyridoxal 5'-phosphate (PLP) in serum/plasma

Published: August 9, 2026Updated: August 16, 2026

This test measures the active form of vitamin B6 (pyridoxal 5'-phosphate) in your blood, which helps your body process certain nutrients and produce important chemicals like neurotransmitters.

Quick summary

["PLP helps your body use protein and convert food into energy; low levels may indicate vitamin B6 deficiency."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
26055-4
Short code
Vit B6 pre 250 mg PN PO SerPl-sCnc
Synonyms
Vit B6 pre 250 mg PN PO SerPl-sCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
20
Ref high
400
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82670
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

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms of vitamin B6 deficiency, such as nerve problems, skin changes, or unusual fatigue. It may also be used to monitor vitamin B6 levels in people with certain medical conditions or those taking supplements.

What to Expect Before the Test

No special preparation is needed. You may have blood drawn from a vein in your arm, similar to other blood tests. If you’re on blood thinners or have a history of bleeding issues, let your provider know.

What the Results Mean

Results are interpreted based on your overall health and symptoms. Very low levels may suggest vitamin B6 deficiency, while very high levels could indicate certain metabolic disorders or medication use. Your provider will discuss findings with you.

Common Causes of Abnormal Results

Low PLP levels may be linked to poor diet, certain medications (like anticonvulsants), or conditions affecting nutrient absorption. High levels could result from overuse of supplements or rare genetic disorders.

Reference range

Premenopausal: 20-400 pg/mL; Postmenopausal: <30 pg/mLN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

PLP Level

Frequently asked questions

What symptoms might I experience if my PLP levels are low?
Symptoms of low PLP levels may include nerve pain, weakness, skin rashes, depression, or unusual cravings for unusual foods (like ice or dirt). If you notice these, discuss them with your provider.
How does PLP relate to other vitamin B6 forms?
PLP is the active form of vitamin B6 in your body. Other forms (like pyridoxine) are converted to PLP, but this test specifically measures PLP itself. Your provider may check total vitamin B6 levels if needed.
Can diet alone fix low PLP levels?
Yes, eating foods rich in vitamin B6 (like chicken, fish, nuts, and fortified cereals) can help. If deficiency persists, your provider may recommend supplements or dietary changes under guidance.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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