Valproic Acid, Free & Total Drug Level

Label Mnemonic:	VPAFT
Epic code:	LAB7474
Downtime form:	Doctor/Provider Orders - Pathology Core and Specialty Care Nursery

Commercial Mailout Laboratory
6240-8 RCP
356-8593

Specimen(s):

Serum

Specimen Instructions:

Patient Preparation: Timing of specimen collection: Pre-dose (trough) draw - At steady state concentration.

Separate serum from cells within 2 hours of collection.

Collection Medium:

Red top tube 5 mL (Clot Activator)

Minimum:

Preferred Minimum: 2 mL serum
Absolute Minimum: 1 mL serum

Rejection Criteria:

Light blue (citrate), gray (oxalate), green (heparin), K2EDTA plasma, tubes that contain liquid anticoagulant, or gel separator tubes.

Delivery Instructions:

Deliver to laboratory immediately after collection.

Turn Around Time:

1-4 days upon receipt at reference laboratory

Reference Range:

Valproic Acid, Total
  Therapeutic Range: 50-125 μg/mL
  Toxic: Greater than 150 μg/mL 

Valproic Acid, Free
  Therapeutic Range: 7-23 μg/mL
  Toxic: Greater than 30 μg/mL 

Valproic Acid, Percent Free
  5-18%

Interpretive Data:

Free valproic acid may be important to monitor in patients with altered or unpredictable protein binding capacity because valproic acid exhibits variable, dose-dependent protein binding. Valproic acid is also subject to drug-drug interactions due to displacement of protein binding. Calculating percent free attempts to minimize differences in test cross-reactivity and may be useful in dose optimization. Adverse effects may include headache, somnolence and dizziness.

Methodology:

Quantitative Enzyme Multiplied Immunoassay Technique

CPT Code:

80164, 80165

See also:
Valproic Acid Drug Level, Plasma