Phenytoin (Dilantin) Concentration in Serum
This test measures the amount of phenytoin, a medication used to control certain types of seizures, in your blood. It helps doctors monitor your dose to balance effectiveness and side effects.
["This test ensures your seizure medication is at a safe and effective level."]
Key facts at a glance
- LOINC
- 94103-9
- Short code
- Zolpidem phenyl-4-carb Ur Ql Scn
- Synonyms
- Zolpidem phenyl-4-carb Ur Ql Scn
- Category
- chemistry
- Sample
- urine
- Container
- Sterile urine container
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- screen
- Specimen volume
- 10 mL
- Stability
- Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 4–24 hours
- Order
- routine
Why This Test Is Done
Your doctor may order a phenytoin test if you’re taking phenytoin (brand names include Dilantin, Phenytek) to manage epilepsy or other seizure disorders. It’s also used to check if your medication levels are within a safe range, especially if you’re taking other medications that might affect how phenytoin works in your body.
What to Expect Before the Test
No special preparation is needed for this blood test. You may have a small needle inserted into your arm or hand to draw a blood sample. If you’re on a blood thinner, let your doctor know before the test.
What Happens During the Test
A healthcare provider will clean the area with an antiseptic, insert a needle into your vein, and collect a small amount of blood. The process usually takes a few minutes. You may feel a slight pinch or sting, but it’s generally over quickly.
What the Results Mean
Results are used to determine if your phenytoin levels are too high or too low. High levels can cause side effects like dizziness, confusion, or skin rashes, while low levels may not control seizures effectively. Your doctor will discuss these results with you and adjust your medication if needed.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Phenytoin is a critical medication for managing epilepsy, but maintaining proper blood levels is essential. Too little can lead to seizures, while too much can cause serious side effects like liver damage, heart rhythm issues, or even coma. Regular monitoring helps prevent these risks and ensures your treatment remains safe and effective.
Short name
Phenytoin Level
Frequently asked questions
How often should I get this test?
What are the common side effects of phenytoin?
Can I drink alcohol while taking phenytoin?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy