Valproic acid
At a Glance
Why Get Tested?
When to Get Tested?
Sample Required?
Test Preparation Needed?
The Test Sample
What is being tested?
Seizure disorders affect the brain’s ability to transmit electrical impulses and to regulate nerve activity. During a seizure, a patient may experience changes in consciousness, alterations in sight, smell and taste, and may experience convulsions. Seizures are associated with acute conditions, such as high fevers, head trauma, severe infections and exposure to toxins, and with chronic conditions such as metabolic disorders and brain tumours. In many cases the cause is not known. The frequency of seizures varies from a single episode, to occasional seizures, to recurrent. Rarely, a patient may have a seizure that does not stop without prompt medical intervention. People may experience some fatigue and a short period of confusion after a seizure. Muscle contractions during a seizure can lead to an injury and, in some cases, recurrent seizures can eventually lead to progressive brain damage. For most people there will be little or no residual damage.
Bipolar disorder is a mental condition that is characterised by cycles of depression and mania that may last for days, weeks, months, or years. During a depressive episode those affected may feel sad, hopeless, worthless and have thoughts of suicide. During a manic episode, those affected may be euphoric, irritable, use poor judgment and participate in risky behaviours. Valproic acid is prescribed to help even out the moods of the person with bipolar disorder, especially mania. It is also given to some patients with recurrent migraine headaches, not so much as to treat migraines but to help prevent their occurrence.
Valproic acid levels must be maintained within a narrow therapeutic range. Too little and the patient may experience a recurrence of symptoms (seizures, mania or migraines); too much and the patient may experience increased side effects. This balance is not always easily achieved. The drug is metabolised by the liver and is processed at a rate that varies from patient to patient and is affected by a patient’s age and the health of their liver. In addition, valproic acid levels are often affected by other drugs such as carbamazepine, phenytoin, lamotrigine, and phenobarbitone. They increase the rate of valproic acid metabolism, thus decreasing its concentration in the blood.
Dosages of valproic acid must be adjusted carefully until a steady concentration in the blood is reached. The actual amount of drug that it takes to reach this steady state will vary from person to person and may change over time.
How is the sample collected for testing?
Is any test preparation needed to ensure the quality of the sample?
The Test
How is it used?
- Gastrointestinal symptoms such as nausea, vomiting, diarrhoea
- Dizziness
- Unusual weight gain or loss
- Tremors
- Blurred or double vision, uncontrolled eye movements
- Mood swings
- Unusual bruising and bleeding
- Hives
- Hair loss
- Rare complications such as liver dysfunction or pancreatitis
Very young and elderly patients are more likely to experience increased side effects. In some cases, the severity of side effects may cause the patient and doctor to seek another anti-seizure, bipolar, or migraine medication.
When is it requested?
The test may be ordered when a patient’s condition does not appear to be responding to valproic acid to determine whether concentrations are too low, the medication is ineffective, and/or to determine if the patient is complying with therapy (taking the valproic acid regularly). It may also be ordered when a patient experiences a troublesome level of side effects and/or develops complications.
Patients should talk to their doctor about the timing of the sample collection. Since dosage timing varies, and some formulations are time released, collection specifics may vary. Often, the recommended time for sample collection is just before the next dose is taken (trough level). This ensures that the minimum amount of drug to be effective is maintained in the blood.
What does the test result mean?
In general, if valproic acid results are within the therapeutic range, the patient is not having recurrent seizures, mood swings or migraines, and the patient is not experiencing significant side effects, then the dosage of valproic acid a patient is receiving is considered adequate. Patients should not increase, decrease, or stop taking their medication without consulting with their doctor as it can increase their risk of having a seizure and may affect other medications that they are taking. Dosage determinations and adjustments must be evaluated on a case-by-case basis.
Is there anything else I should know?
While severe liver injury is rare, mild increases in liver-related enzymes (AST and ALT) occur in up to 20% of those taking valproic acid; these usually return to normal even if the drug is continued.
The fetus of women who use valproic acid during pregnancy are at an increased risk of developing several birth defects. Since this drug increases the risk of neural tube defectssuch as spina bifida, women of child-bearing age who want to become pregnant should talk to their doctors about this subject.
A variety of prescribed drugs, over-the-counter medications and supplements can increase, decrease, or interfere with the concentrations of valproic acid in the blood. Patients should talk to their doctors about all of the drugs and supplements that they are taking and about the medication(s) that are right for them. Valproic acid is not effective for every kind of seizure and will not work for every patient.
Common Questions
Ask a Laboratory Scientist
Article Sources
NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
