Valproic Acid, Free & Total Drug Level
Label Mnemonic: VPAFT
Epic Lab Code: LAB7474
Downtime Form: A-1a Miscellaneous Request
Commercial Mail-out Laboratory
5231 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 VPA- % 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:
80165
 
See also:
Valproic Acid Drug Level, Plasma