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Test Code VALPA Valproic Acid, Total, Serum

Useful For

Monitoring total valproic acid in therapy

 

Assessing compliance

 

Evaluating potential toxicity

Method Name

Immunoassay

Reporting Name

Valproic Acid, Tot, S

Specimen Type

Serum


Specimen Required


Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL

Collection Instructions:

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

2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.


Specimen Minimum Volume

0.25 mL

Specimen Stability Information

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

Reject Due To

Hemolysis

Mild OK; Gross reject

Lipemia

NA

Icterus

NA

Other

NA

Clinical Information

Valproic acid (valproate, Depakote, or Depakene) is used for treatment of simple and complex absence seizures and as combination therapy with other anticonvulsants for control of generalized seizures that include absence seizures.

 

Valproic acid is initially dosed at 15 mg/kg/day, with dosage increases over time to a maximum of 60 mg/kg/day. The volume of distribution of valproic acid is 0.2 L/kg and its half-life is 10 to 14 hours in adults, and shorter in children. It is approximately 90% protein bound.

 

Hepatic failure and a Reyes-like syndrome associated with administration of valproic acid at therapeutic levels have been reported. Careful monitoring of liver function during the first 6 months of therapy is required. Major side effects such as central nervous system depression, thrombocytopenia, and hepatic dysfunction are likely to be experienced if the peak level regularly is above 125 mcg/mL.

 

Analysis of free valproic acid levels may be useful in delineating the cause of toxicity when the total concentration is not excessive.

 

Valproic acid exhibits substantial effects on the pharmacology of phenytoin, whereas phenytoin exhibits only a limited effect on valproic acid. This is due to the relative abundance of the 2 drugs in the body. Valproic acid is present at a 2- to 3-fold mass excess and a 5- to 7-fold molar excess.

Reference Values

Therapeutic: 50 (trough)-125 (peak) mcg/mL

Critical value: ≥151 mcg/mL

Interpretation

Optimal response is usually observed when the trough level is above 50 mcg/mL.

 

Peak levels should not exceed 125 mcg/mL.

Clinical Reference

1. Cotariu D, Zaidman JL: Valproic acid and the liver. Clin Chem 1988;34:890-897

2. Moyer TP: Therapeutic drug monitoring. In Tietz Textbook of Clinical Chemistry. Edited by CA Burtis, ER Ashwood. Fourth edition. WB Saunders Company. Philadelphia, 2005, pp 1237-1285

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Analytic Time

Same day/1 day

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

80164

LOINC Code Information

Test ID Test Order Name Order LOINC Value
VALPA Valproic Acid, Tot, S 4086-5

 

Result ID Test Result Name Result LOINC Value
VALPA Valproic Acid, Tot, S 4086-5

Secondary ID

37066