Valproic acid
Biochemistry
Royal Stoke University Hospital
Pre-analytical information
Add-on requests: up to 7 days post sampling
Minimum Retest Interval: 7 days
Collect the blood sample using normal venepuncture technique into a gel serum or plain serum tube (yellow or red-top).
Samples should be sent to the laboratory on the same day as collection to ensure sample integrity is maintained. If a delay in receipt of the sample is anticipated, please contact the laboratory to discuss storage requirements.
Stable in separated serum for 2 days at room temperature and 7 days at 4-8oC.
For generic information on test requesting, sample labelling and packaging, and sample transport – see the frequently asked questions here.
Adult sample type:
Paediatric sample type:
Plain serum
Based on receipt at testing site.
Within 24 hours.
There is a tentative target therapeutic range of 50-100 mg/L, but patients may respond better at lower or higher levels.
Results outside the reference range do not necessarily indicate disease. Similarly, results within the reference range do not preclude abnormality. Please contact the Duty Biochemist for discussion of individual patient results.
Valproate is an anticonvulsant that was previously used as first-line therapy in epilepsy, for mood stabilisation in bipolar disorder/dementia and prophylaxis of migraine and neurogenic pain. However, the use of valproate is now highly restricted due to the risk of adverse side effects.
Measurement of valproate is not generally recommended as there is little evidence for a target range and plasma concentrations are no better guide to clinical response than the dose. If it is decided valproate measurement is required for a particular patient (e.g. due to suspected drug toxicity or non-adherence with therapy), the sample should ideally be taken 2 to 4 hours post dose.
Factors that significantly affect result
Valproate clearance is slower during fasting because free fatty acids displace the drug from albumin inhibiting its metabolism. Carbapenem antibiotics (e.g. meropenem), lamotrigine and enzyme-inducing anticonvulsants (e.g. carbamazepine, phenytoin, phenobarbital) increase valproate clearance to varying extents by different mechanisms.
There are a number of non-pathological factors that can influence levels of specific analytes, giving falsely elevated or reduced levels. If you require more information regarding the effects of these factors on the individual test results, please contact the Duty Biochemist.
Serum/plasma samples are routinely screened for the presence of haemolysis, icterus and lipaemia. Results are not reported if one or more of these has been detected at levels deemed to have had a significant impact on the accuracy of the test.
For more information on valproate, please see the following: https://labtestsonline.org.uk/tests/valproic-acid
Reviewed / Updated On: 02/12/2025
