This test measures the amount of the drug carbamazepine in your blood. Carbamazepine is the generic name of a drug used to treat epilepsy, mania, bipolar disorder, and pain. Brand names include Tegretol, Carbatrol, and Equetro.
Certain people have serious but rare skin reactions during the first four months of taking this drug. Some of these reactions can be fatal. The FDA says that people at risk for these reactions have a specific marker in their blood, HLA-B*1502, also called the human leukocyte antigen allele. Most people who have this marker are of Asian descent. The FDA recommends that doctors screen patients for this marker before prescribing it.
If you take this drug for a period of time, you may also become increasingly sensitive to its effects, which can cause it to be toxic to your system. Your doctor can use this test to monitor the amount of the drug in your body to make sure that it doesn't reach a toxic level.
You may have this test to look at the level of carbamazepine in your body. In addition to causing rare but serious skin and blood reactions, carbamazepine can sometimes cause people to have suicidal thoughts.
Call your health care provider if you have these symptoms while taking the drug:
Fever, sore throat, or other infections
Skin that bruises easily
Red or purple spots on the skin
Severe fatigue or weakness
Your doctor may also order other tests, including:
Liver function tests to look for liver damage
Complete blood count, with differential to find out the amount of certain types of blood cells
Electrolyte test to measure the levels of certain minerals in your blood
Blood urea nitrogen, or BUN, and creatinine tests to find out if your kidneys are working normally
You will also have genetic testing before starting this drug to find out how likely you are to have a serious reaction to it.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Results are given in micrograms per milliliter (mcg/mL) or micromoles per liter (micromol/L). Safe blood levels of carbamazepine are 4 to 12 mcg/mL, or 17 to 51 micromol/L. You may fall into a coma or have other health problems if your levels are above 40 mg/mL, or 170 micromol/L.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Timing is important for this test. The most accurate results are usually from a test done just before you take a scheduled dose of carbamazepine.
Tell your doctor how long you've been taking carbamazepine and what blood level has been adequate to control your symptoms in the past. Also be sure your doctor knows about all other medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.