Tricyclic antidepressant (TCA) testing
This test is used to check a sample of blood or urine for tricyclic antidepressants (TCAs). Healthcare providers prescribe these medicines for depression and a number of other problems. These include anxiety, headaches, and nerve-related pain.
These medicines can be helpful in normal doses. But taking too much can be fatal. These medicines are often the cause of death in prescription-medicine overdoses in the U.S.
You may need this test to help your healthcare provider prescribe the proper dose of a TCA. Healthcare providers may also do this test if you have symptoms that may point to taking too much of one of these medicines.
Symptoms of overdose include:
Serious changes in heart rhythm
Low blood pressure
Body temperature that is too high (hyperthermia)
If your healthcare provider suspects that you have taken too much of one of these medicines, he or she may do an electrocardiogram to check your heart's rhythm. Your provider may also order other blood tests. These include a complete blood count, creatinine, electrolytes, and blood sugar. He or she will also check for other substances that are commonly taken along with a TCA overdose.
A result for a lab test may be affected by many things, including the method the laboratory uses to do the test. 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 healthcare provider.
Depending on the tricyclic antidepressant medicine you are taking, the level for treatment will range from 50 to 250 nanograms per milliliter (ng/mL). Toxic levels are above 300 to 500 ng/mL.
The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. Or it is done with a urine sample, which is usually provided by urinating into a cup. The result of a urine test for TCAs will be reported only as negative or positive.
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.
Some other medicines can interfere with this test, causing a false-positive for TCAs. These include carbamazepine, quetiapine, diphenhydramine, thioridazine, chlorpromazine, and cyclobenzaprine.
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.