Test Overview

A medicine blood level test measures how much of your medicine is in your blood. Your doctor checks it to make sure that you are taking a safe and effective dose. This testing is also called therapeutic drug monitoring.

Why It Is Done

Seizure medicines are usually monitored because:

• At a low blood level, they don't control seizures as well as they should.
• At a high blood level, they may cause problems.

Your doctor may use your test results to adjust your dose.

You may need testing when you take a seizure medicine such as:

• Carbamazepine.
• Clozapine.
• Levetiracetam.
• Phenobarbital.
• Phenytoin.
• Valproic acid.

When these medicines are used to treat bipolar disorder, nerve pain, or migraine headaches, testing for low levels isn't as common as for seizures.

How To Prepare

Depending on which medicine you take, your doctor may schedule your test at a certain time of day. For example, your test may be done right before you take a dose of medicine.

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

A medicine blood level test measures how much of your medicine is in your blood. Your doctor checks it to make sure that you're taking a safe and effective dose. This testing is also called therapeutic drug monitoring.

The medicine blood level is just a guide. Your doctor will also look at your results based on your age, health, and other factors to help decide whether you are taking the right amount of medicine.