Valproic Acid

Diagnostic Use

Valproic acid (valproate) is an antiepileptic drug.

Under normal physiological circumstances, 90-95% of the measured circulating valproate is bound to plasma proteins. A free (unbound) valproate assay is also available and may provide useful additional information in those with an abnormal plasma protein concentration, or in those taking additional protein-bound drugs.

Department

Core Biochemistry

Delphic Registration Code

VALP

Synonyms

Epilim
Valproate

For a full list of brand names for this drug used in NZ, please see the relevant entry in the NZ Formulary

Turnaround Time

3 hours

Test Code

4810

Specimen Type

• Serum
• Plasma

Specimen Requirements

Tube/Container Type:

Preferred

• Lithium Heparin - Non-gel (Green Cap)

Acceptable

• Serum (Red Cap)

Preferred Sample Volume (ml)

4.5

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• Lithium Heparin - Non-gel (Green Cap)

Acceptable

• Serum (Red Cap)

Preferred Sample Volume (ml)

0.6

Additional Specimen Information

A trough sample should be collected (i.e. taken immediately before the next dose is due).

Aliquot Instructions

Sample Type

• Serum
• Plasma

Minimum Volume (ml)

0.5

Transport to Lab

Chilled (2 - 8 degrees Celsius)
If overnight - Chilled (2 - 8 degrees Celsius)

Additional Referral/Aliquot Information

Samples are stable for 48 hrs at fridge temperature.
Frozen samples are stable for up to 7 days.

Interpretation

The standard half-life of sodium valproate is 12 hours, with time to steady-state of 3 days.

Refer to the CDHB Therapeutic Drug Monitoring Profiles for advice on how to interpret valproate levels.

Reference Intervals

 

Test	Therapeutic range
Valproate	350-700μmol/L
Free (unbound) valproate	35-70μmol/L

The above range is a guide only.  The target plasma concentration should be tailored to the individual patient in accordance with clinical features of efficacy and/or drug toxicity.  Consultation with the clinical pharmacology team is recommended if expert advice is required.

Test Method

Homogenous enzyme immunoassay performed on the Beckman Coulter AU5822 analyser using Beckman Coulter reagents.

Non-Funded Test Cost

$23.74 (Exclusive of GST)

Billing Code

4810

Contact Information

Enquiry Form