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Test Code VALPF Valproic Acid, Free, Serum

Useful For

Monitoring free valproic acid in therapy

 

Assessing compliance

 

Evaluating potential toxicity

Method Name

Ultrafiltration Followed by Immunoassay

Reporting Name

Valproic Acid, Free, S

Specimen Type

Serum


Specimen Required


Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 2 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged, and the serum aliquoted into a plastic vial within 2 hours of collection.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 14 days
  Frozen  28 days
  Ambient  72 hours

Reject Due To

Gross hemolysis Reject

Clinical Information

Valproate (valproate, Depakote, or Depakene) is an effective medication for absence seizures, generalized tonic-clonic seizures, and partial seizures, when administered alone or in conjunction with other antiepileptic agents.

 

The valproic acid that circulates in blood is 85% to 90% protein-bound under normal circumstances. In uremia or during concomitant therapy with other drugs that are highly protein-bound (such as phenytoin), valproic acid is displaced from protein, resulting in a higher free fraction of the drug circulating in blood.

 

Since neurologic activity and toxicity of valproic acid are directly related to the unbound fraction of drug, adjustment of dosage based on knowledge of the free valproic acid concentration may be useful in the following: concomitant use of highly protein-bound drugs (usually >80% bound), hypoalbuminemia, pregnancy, kidney or liver failure, and in older adults. In these situations, the total valproic acid concentration in the blood may underestimate the disproportionately higher free valproic acid fraction.

Reference Values

Therapeutic: 5-25 mcg/mL

Critical value: >30 mcg/mL

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 day

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

80165

Forms

If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.