To measure the amount of valproic acid in the blood and to maintain an effective level
To detect low or excessive (potentially toxic) levels
A blood sample taken from a vein in your arm
This test measures the amount of valproic acid in the blood. Valproic acid is a drug that is used mainly to treat certain fitting disorders (also called seizures or epilepsy), but is also prescribed to treat bipolar disease (manic depression) and to prevent migraine headaches, though this is an unlicensed use of valproic acid in the UK. It may be used in combination with other antiepileptic drugs such as phenytoin or carbamazepine to control certain kinds of seizures.
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 fits. Seizures can occur with rapidly developing conditions, such as high fevers, head trauma, severe infections, and exposure to toxins, and with long-term diseases 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, or frequent seizures. Rarely, a patient may have a seizure that does not stop without prompt medical treatment. People may experience some tiredness and a short period of confusion after a seizure. Muscles contract during a seizure and can lead to an injury and, in some cases, recurrent seizures can eventually lead to continuing brain damage, but for most people there will be little or no residual damage. Anti-seizure medications such as valproic acid may be prescribed to reduce the frequency and severity of seizures.
Bipolar disorder is a mental disease that has 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 may also be given to some patients with recurrent migraine headaches, not to treat an acute attack but to help prevent attacks.
Valproic acid levels in the blood must be maintained within certain limits. Too little and the patient may have more symptoms (seizures, mood swings, or migraines); too much and the patient may have increased side effects. This balance is not always easily achieved. The drug is broken down by the liver, but the rate 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 phenobarbital. These drugs increase the rate that valproic acid is broken down and therefore reduces its levels in the blood.
Monitoring of blood levels may be more important when someone is taking more than one drug.
The dose of valproic acid must be adjusted until a suitable concentration in the blood is reached. The amount of drug that is required to reach a steady state will vary from person to person and may change over time. Measuring the valproate level in the blood may help in this process in some cases, but is not often necessary.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
The valproic acid test may be used to measure and monitor the amount of valproic acid in the blood to find out whether drug levels are appropriate. The amount of the drug taken may be changed depending on the results of the blood test. The test may then be checked occasionally to ensure that therapeutic blood levels are maintained. One or more valproic acid tests may be requested if a patient starts or stops taking additional medications (to judge their effect, if any, on valproic acid levels) and may be used if the patient has a recurrence of symptoms such as a seizure, a migraine, or experiences bipolar mood swings. Doctors will also evaluate their patient for side effects and adverse reactions during initial dosage adjustments and over time. These side effects may include some or a combination of the following:
- Gastrointestinal symptoms such as nausea, vomiting, diarrhoea
- Unusual weight gain or loss
- Tremors (shaking)
- Drowsiness or lethargy
- Mood swings
- Unusual bruising and bleeding
- Itchy rash
- Hair loss (transient)
- 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 an alternative medicine.
When is it requested?
Routine monitoring is generally unnecessary, but a valproic acid level may be requested when a patient begins valproic acid treatment and when/if a patient’s drugs are started, stopped, or changed.
The test may be requested when a patient’s condition does not appear to be responding to valproic acid to find out whether levels are too low, the medicine is ineffective, and/or to find out if the patient is taking the prescribed dose of valproic acid regularly. It may also be requested 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 of the drug release the drug slowly over time, times of specimen collection 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?
The appropriate range for valproic acid in the blood is usually taken as 50 - 120 mg/L (350-835 µmol/L). Within this range, most people will respond to the drug without excessive side effects; however, response varies with each individual. Some people will experience seizures, mood swings, or migraines at the low end of the therapeutic range while some people will experience excessive side effects at the upper end. Patients should work closely with their doctor to find the dose and level that works the best for them.
In general, if valproic acid results are within the target 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. Dose adjustments must be made on a case-by-case basis.
Is there anything else I should know?
Valproic acid reduces the breakdown of other seizure medicines such as carbamazepine, phenytoin, lamotrigine, and phenobarbital, and increase their levels in the blood. If a patient is on additional drugs such as these, they may occasionally need to be monitored with blood tests.
While severe liver injury is rare, mild increases in enzymes (AST and ALT) which come from the liver occur in up to 20% of those taking valproic acid; these usually return to normal even if the drug is continued.
The babies 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 defects such 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 medicine, 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 medicines that are right for them. Valproic acid is not effective for every kind of seizure and will not work for every patient.
How long will I need to be on valproic acid?
Valproic acid is usually taken every day (sometimes several times a day) for a patient’s lifetime. An exception to this may be patients whose seizures are caused by a temporary condition; they may only need the medication for a short period of time.
How is valproic acid taken?
It may be taken as a tablet, slow release tablet, a liquid, or sprinkled on a soft, cold food. It is generally taken with food to minimise stomach upset, and it is important that the solid forms be swallowed not chewed to avoid mouth and throat irritation.
Can I test my valproic acid level at home?
No, it requires specialised equipment. Blood samples are collected from a vein in the arm and tested in the laboratory.