The Test Sample
What is being tested?
Valproic acid is a drug that is used primarily to control certain seizures by lessening their severity and frequency. It may be prescribed in combination with other antiepileptic drugs such as phenytoin or phenobarbital. The valproic acid level in the blood must be maintained within a narrow therapeutic range. This test measures the level of valproic acid in the blood.
Seizure disorders affect the brain's ability to transmit electrical impulses and to regulate nerve activity. During a seizure, someone may experience changes in consciousness, alterations in sight, smell, and taste, and may experience convulsions. Seizures are associated with several conditions but, in many cases, the cause is not known. The frequency of seizures varies from a single episode, to frequent, recurrent seizures. Rarely, someone 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 but, for most people, there will be little or no residual damage.
Sometimes valproic acid is prescribed for bipolar disorder, a psychiatric condition characterized 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 behaviors. Valproic acid is prescribed to help even out the moods, especially those of mania, of the person with bipolar disorder. The drug is also used to treat people with recurrent migraine headaches to help prevent their occurrence and to treat certain chronic pain syndromes.
The valproic acid level in the blood must be maintained within a narrow therapeutic range. If the level is too low, someone may experience a recurrence of symptoms, but, if the level is too high, someone may experience an increase in the number and severity of symptoms and side effects. The balance is often difficult to achieve because the drug is metabolized by the liver and is processed at a rate that varies from person to person and is affected by age and liver health.
Most valproic acid is bound to protein in the blood and it is the unbound "free" portion that is active. If someone has a condition that results in a lower than normal amount of protein in their blood, then that person may have an excess of active "free" valproic acid.
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?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No special test preparation is needed, but patients should talk to their health care provider about the timing of the sample collection. Since dosage timing varies and some formulations are time-released, collection specifics may vary. Often, sample collection is recommended for when levels are at their lowest (trough level). This ensures that the minimum amount of drug to be effective is maintained in the blood.