This test measures the amount of the medicine carbamazepine in your blood. Carbamazepine is the generic name of a medicine used to treat epilepsy, mania, bipolar disorder, and pain.
Certain people have serious but rare skin reactions during the first 4 months of taking this medicine. 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 healthcare providers screen patients (especially those of Asian descent) for this marker before prescribing it.
If you take this medicine for a period of time, you may also become increasingly sensitive to its effects. This can cause the medicine to be toxic to your system. Your healthcare provider can use this test to monitor the amount of the medicine in your body to make sure that it doesn't reach a toxic level. Do not stop this medicine suddenly. Stopping this medicine suddenly may cause serious problems.
You may need this test if your healthcare provider wants 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 healthcare provider if you have these symptoms while taking the medicine:
Fever, sore throat, or other infections
Skin that bruises easily
Red or purple spots on the skin
Severe fatigue or weakness
Difficulty sleeping (insomnia)
Nausea, vomiting, or belly pain
Yellowing of the eyes or skin (jaundice)
Shortness of breath
Fast, slow, or pounding heartbeat
Any new symptoms of mental illness, including anxiety, depression, or suicidal thoughts
Any worsening of existing mental illness, including anxiety, depression, or suicidal thoughts
Your healthcare provider 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
Levels of other medicines you may be taking
You may also have genetic testing before starting this medicine to find out how likely you are to have a serious reaction to it. Your healthcare provider may suggest this if you have an ethnic background that puts you at risk.
Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
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 is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.
Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be 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 healthcare provider how long you've been taking carbamazepine and what blood level has been adequate to control your symptoms in the past. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.