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Free Valproate (Valproic Acid), Serum/Plasma — Substance Concentration

Published: August 9, 2026Updated: August 17, 2026

Measures the unbound portion of valproate in serum or plasma, which is the fraction available to the brain and other tissues.

Quick summary

["This test measures active, unbound valproate and may help guide dosing when total levels are difficult to interpret."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
32119-0
Short code
Valproate Free SerPl-sCnc
Synonyms
Valproate Free SerPl-sCnc
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
44
Ref high
147
Critical range
— – 151 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84075
SNOMED
27550007
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 is this test?

This blood test measures free valproate, also called free valproic acid. Some valproate in the blood is bound to proteins, while the free portion is not bound and is available to affect the body.

Why might I need this test?

Your clinician may order this test to monitor valproate treatment, especially when symptoms or side effects do not match the expected total valproate level. It can also be helpful when protein levels or other factors that affect drug binding are unusual.

How is the test performed?

A blood sample is drawn from a vein and analyzed in the laboratory. The report provides the concentration of free valproate in the sample.

How do I prepare for the test?

Follow your clinician's instructions about when to take valproate before the blood draw. Inform the laboratory if you are pregnant or have low blood protein, and do not change or stop your medication without medical advice.

Reference range

Adult: 44-147 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free valproate

Frequently asked questions

How is free valproate different from a total valproate level?
The total level includes both protein-bound and free valproate, while the free test measures only the unbound portion available to the body. The two results may not always rise and fall together.
Why might my clinician order both total and free valproate tests?
Comparing both results can help determine whether an unusual total level reflects a change in protein binding or a change in the amount of active, free drug.
Does an abnormal free valproate result mean I should change my dose?
Not by itself. Your clinician should interpret the result with your symptoms, other laboratory findings, and medication history before making any dosing changes.
  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 17, 2026. · Read our editorial policy