Valproic Acid (VPA) |
EPIC Test Name
VALPROIC ACID LEVEL, TOTALEPIC Code
LAB24Specimen Requirements
plasma | |
---|---|
Minimum Volume: | 0.5 mL |
Collection: | Collect using standard laboratory procedures |
Transport: | Room Temperature ASAP |
Stability: | Room Temperature: 2 days capped at 15-25 degrees C Refrigerated: 7 days capped at 2-8 degrees C Frozen: 3 months capped at -20 degrees C Avoid repeat freezing and thawing |
Container: | LIT-GRN |
Rejection Causes: | Insufficent Sample Volume |
Methods
Homogeneous enzyme immunoassayTurnaround Time
Specimen | Turnaround Time | Frequency |
---|---|---|
plasma | Stat: 90 minutes Routine: 4 hours | 24/7 |
Reference Ranges
Homogeneous enzyme immunoassay
Unit | Critical Values | Therapeutic Levels |
---|---|---|
µg/mL | >120 ug/mL | 50-100 µg/mL |
Clinical Indications
Valproic acid (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. It also has mood-stabilizing effects that make it a useful agent in the treatment of bipolar disorder.Valproic acid inhibits the enzyme GABA transaminase, resulting in an increase in the concentration of GABA in the brain. GABA is a potent inhibitor of discharges in the central nervous system. It also modulates the synaptic sodium channel by prolonging inactivation, which reduces the ability of the neuron to respond at high frequency. Additional mechanisms of action have been reported, such as GSK-3 activity that might explain its utility in mood disorders.
The valproic acid that circulates in blood is around 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. As a result, even the total drug concentration may be within the therapeutic range, the portion of the free drug may be in toxic level. Because the pharmacokinetics of the drug can be extensively influenced by other drugs, e.g., phenobarbital, phenytoin and lamotrigine, proper dose adjustment and monitoring its blood concentration are important to avoid adverse event and toxicity.
Common Synonyms
Depakote, Depakene Depakane, Depakene, Depakote, DivalproexPerformed
Lab |
---|
Chemistry - Community |
Chemistry - Downtown |
Interpretative Information
The range for therapeutic concentration of total valproic acid is 50 to 100 mcg/mL.Low valproic acid concentration relative to these ranges may suggest inadequate dosing, while a high valproic acid concentration may be associated with hepatic toxicity and acute toxic encephalopathy.
Because the concentration of valproic acid fluctuates considerably depending on the time from last dose, interpretation of the clinical significance of the valproic acid concentration must take into consideration the timing of the blood specimen. The ideal time for monitoring the blood concentration is to drawn just before the next dose, to confirm that an adequate dose has been prescribed.
CPT
80164LOINC
4086-5References
1. Ghodke-Puranik Y, Thorn CF, Lamba JK, Leeder JS, Song W, Birnbaum AK, Altman RB, Klein TE. Valproic acid pathway: pharmacokinetics and pharmacodynamics. Pharmacogenet Genomics. 2013 Apr;2. Michael C. Milone and Leslie M. Shaw: Therapeutic Drugs and Their Management. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier Saunders; 2018:813-815
3. Marzinke A and Clarke W. Antiepileptic drugs. In The Clinical Toxicology Laboratory – contemporary practice of poisoning evaluation. ed. by Tai Kwong, etc., 2nd ed. Page 235-60.
Contact Information
Chemistry - Downtown: (315)464-4460Chemistry - Community: (315)492-5531