Adult patient:
Heparin gel tube
Minimum blood volume: 5 mL
Paediatric patient:
Paediatric heparin tube
Number of vials: 1
Minimum blood volume: 1.3 mL
Authorisation code required
No
24 Hr available service
Yes
(Call extension: 3353 for express result)
Precaution
Blood should be taken just prior to dose, preferably in the fasting state.
Method
Immunoassay
Reference interval
Therapeutic range: 346 - 693 µmol/L
(Source: from manufacturer's kit insert)
Clinical indication
Therapeutic drug monitoring
Result interpretation
Several factors complicate interpretation of valproate levels, including time interval between drug administration and blood sampling, the type of seizures treated, albumin concentration and factors affecting albumin binding of valproate, and the presence of other anti-epileptic drugs and pharmacologically-active metabolites of valproate.
Occasionally, hepatotoxicity may occur with serum levels < 700 µmol/L (< 100 mg/L).
The half-life is about 6 - 20 Hr, but is shorter when valproate is given in combination with other anticonvulsants.
Measurement of uncertainty
Frequency of measurement
Daily