Good to knowOne result rarely tells the whole story. Your provider looks at your results together with your symptoms, exam, and other tests.
What the test is
Usually drawn right before your next dose (a 'trough').
Why it's done
- Starting or changing a dose
- Breakthrough seizures
- Side effects like unsteadiness or confusion
- Pregnancy or new interacting medicines
Getting ready and what happens
- Draw right before your next dose unless told otherwise.
How the test is done
- A health worker cleans the skin, puts a band around your arm, and draws blood from a vein with a small needle. It takes a few minutes.
What the results mean
| Result | Typical range for adults |
|---|---|
| Phenytoin (total) | About 10 to 20 mcg/mL |
| Valproic acid | About 50 to 100 mcg/mL |
| Carbamazepine | About 4 to 12 mcg/mL |
Normal ranges vary from lab to lab and can differ by age, sex, and pregnancy. Your report lists your lab's own range next to each result. A result a little outside the range is often not a problem.
Results
Your provider adjusts the dose based on levels, seizure control, and side effects.
Questions to ask your provider
- What do my results mean for me?
- Do I need to repeat this test or have other tests?
Risks
A blood draw is very safe. You may have slight pain or a small bruise where the needle went in.
Related conditions
Related medicines
Related tests
Sources
Last updated 2026-11-13.