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Test Code VALPG Valproic Acid, Free and Total, Serum

Reporting Name

Valproic Acid, Free and Total, S

Useful For

Monitoring both total and free valproic acid levels in therapy

 

Assessing compliance

 

Evaluating potential toxicity

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum


Specimen Required


Container/Tube:

Preferred: Serum gel

Acceptable: Red top

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 aliquoted 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

Reference Values

VALPROIC ACID, TOTAL

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

Critical value: ≥151 mcg/mL

 

VALPROIC ACID, FREE

Therapeutic: 5-25 mcg/mL

Critical value: >30 mcg/mL

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

CPT Code Information

VALPA – 80164

VALPF - 80165

LOINC Code Information

Test ID Test Order Name Order LOINC Value
VALPG Valproic Acid, Free and Total, S 57775-9

 

Result ID Test Result Name Result LOINC Value
VALPF Valproic Acid, Free, S 4087-3
VALPA Valproic Acid, Tot, S 4086-5

Clinical Reference

1. Cloyd JC, Fischer JH, Kriel RL, Kraus DM: Valproic acid pharmacokinetics in children: Effects of age and antiepileptic drugs on protein binding and intrinsic clearance. Clin Pharmacol Ther 1993;53:22-29

2. Wagner ML, Graves NM, Leppik IE, et al: The effect of felbamate on valproic acid disposition. Clin Pharmacol Ther 1994;56:494-502

3. Dasgupta A, Volk A: Displacement of valproic acid and carbamazepine from protein binding in normal and uremic sera by tolmetin, ibuprofen, and naproxen: presence of inhibitor in uremic serum that blocks valproic acid-naproxen interactions. Ther Drug Monit 1996;18:284-287

4. 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

Method Description

The assay is based on a homogeneous enzyme immunoassay technique used for the quantitative analysis of valproic acid (free and protein-bound) in human serum or plasma. The assay is based on competition between drug in the sample and drug labeled with the enzyme glucose-6-phosphate dehydrogenase (G6PDH) for antibody binding sites. Enzyme activity decreases upon binding to the antibody, so the drug concentration in the sample can be measured in terms of enzyme activity. Active enzyme converts oxidized nicotinamide adenine dinucleotide (NAD) to NADH (the reduced form of NAD), resulting in an absorbance change that is measured spectrophotometrically. Endogenous serum G6PDH does not interfere because the coenzyme functions only with the bacterial (Leuconostocmesenteroides) enzyme employed in the assay.(Package insert: Roche Valproic reagent, Roche Diagnostic Corp, Indianapolis, IN)

Analytic Time

Same day/1 day

Reject Due To

Gross hemolysis Reject

Method Name

VALPA: Immunoassay

VALPF: Ultrafiltration Followed by Immunoassay

Forms

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

Profile Information

Test ID Reporting Name Available Separately Always Performed
VALPF Valproic Acid, Free, S Yes Yes
VALPA Valproic Acid, Tot, S Yes Yes