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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 produce important chemicals involved in metabolism, red blood cell production, and nerve function.

Quick summary

["Vitamin B6 is essential for many bodily functions, and low levels may indicate deficiencies or health concerns."]

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

Key facts at a glance

LOINC
61536-9
Short code
Vit B6 PhenX
Synonyms
Vit B6 PhenX
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
phenx
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 Might Be Ordered

Your doctor may recommend this test if you have symptoms like fatigue, nerve pain, or unusual mood changes, or if you have conditions such as anemia, seizures, or certain genetic disorders. It may also be checked during pregnancy or if you’re taking medications that can affect vitamin B6 levels.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for a few hours before the blood draw, but this depends on your doctor’s instructions. Bring any medications you’re taking to your appointment.

How the Test Works

A small sample of blood is taken from a vein in your arm. The blood is then analyzed in a lab to measure the amount of pyridoxal 5'-phosphate. The test can detect low or high levels of this vitamin, which may signal a deficiency or other health issues.

What the Results Mean

Results are typically reported as a concentration in micrograms per deciliter (µg/dL). While reference ranges vary by lab, very low levels may indicate vitamin B6 deficiency, while very high levels could suggest certain metabolic disorders or medication use.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

PLP Level

Frequently asked questions

What does a low PLP level mean?
Low pyridoxal 5'-phosphate levels may suggest vitamin B6 deficiency, which can cause symptoms like weakness, nerve damage, or anemia. It can also affect how your body processes other vitamins and medications. Your doctor may recommend dietary changes, supplements, or further testing if needed.
What does a high PLP level mean?
High levels of PLP can sometimes occur due to certain medications, metabolic disorders, or genetic conditions. While less common, elevated levels may need monitoring to rule out underlying issues like porphyria or other metabolic imbalances.
How often should I get this test?
This test is usually ordered as needed, depending on your symptoms or medical condition. If you’re at risk for vitamin deficiencies (e.g., due to poor diet, malabsorption, or certain medications), your doctor may recommend periodic checks. Follow their guidance for timing and frequency.
  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