Skip to content

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

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

Measures the unbound, active portion of valproic acid in serum or plasma. This may be helpful when total levels do not fully reflect drug exposure.

Quick summary

["A free valproate level shows how much active medication is available in the blood."]

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

Key facts at a glance

LOINC
4087-3
Short code
Valproate Free SerPl-mCnc
Synonyms
Valproate Free SerPl-mCnc
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. Valproate is partly bound to blood proteins, and only the unbound portion is available to exert its therapeutic effect.

Why might I need this test?

Your clinician may order it to assess valproate treatment when a total valproate level is unexpectedly high or low, or when protein binding may be altered. Factors such as low blood albumin, liver disease, pregnancy, or other medicines can affect the relationship between total and free drug levels.

How is the test performed?

A blood sample is collected, and the amount of free valproate in the serum or plasma is measured. The result is usually interpreted together with your total valproate level, albumin level, symptoms, and medication dose.

How do I prepare for the test?

Take valproate exactly as prescribed and tell your clinician when you last took a dose. Blood collection timing may be important, so follow any instructions about when the sample should be drawn. Do not stop or change 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 Level

Frequently asked questions

What is the difference between a total and free valproate level?
The total level includes both protein-bound and unbound valproate, while the free test measures only the unbound portion available to act on the body. Free levels are especially helpful when protein binding or drug metabolism may be changed.
Is a normal total valproate level always enough?
No. If albumin is low or other factors affect protein binding, the total level may not accurately represent the active amount of valproate. Your clinician may request both total and free levels.
Does the test require a specific collection time?
Sometimes. The level can change depending on when the medication was last taken, so consistent timing and dose information help with interpretation. Follow the timing instructions provided by your clinician or laboratory.
  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