Phenytoin Test
Short Name: Phenytoin
Also known as: Phenytoin Level, Phenytoin Drug Level, Phenytoin Trough Level, Phenytoin TDM
Phenytoin Test test available at DNA Labs India for ₹1,135. Uses Chemiluminescent Immunoassay on Serum samples. Results in Reports are generated daily. You will be notified as soon as the report is available.. Free home collection in 300+ cities across India.
🩺 Medically Reviewed By
Dr Ramarao Paidisetty
Consultant Biochemist · Reg: 21504
Last reviewed: September 7, 2026
Overview
This test is used to monitor the concentration of phenytoin in blood, help evaluate compliance, guide dosage adjustments, and detect phenytoin toxicity.
- Test Code
- 3543
- CPT Code
- 80162
- ICD Code
- Z51.81
- Price
- ₹1,135
- Sample Type
- Serum
- Result Time
- Reports are generated daily. You will be notified as soon as the report is available.
- Fasting Required
- No
- Method
- Chemiluminescent Immunoassay
Sample Collection
Take the sample just before the next oral dose is due, at steady state, unless directed otherwise by your doctor. No fasting is required.
Method: Venipuncture
Laboratory Analysis
A trained phlebotomist will draw blood from a vein in your arm.
Report Delivery
You can resume normal activities and diet immediately after blood collection.
Timeline: Reports are generated daily. You will be notified as soon as the report is available.
Patient Instructions
About This Test
Who Should Get This Test
This test is used to monitor the concentration of phenytoin in blood, help evaluate compliance, guide dosage adjustments, and detect phenytoin toxicity.
How to Prepare
- Recommended specimen: just before the next dose is due at steady state.
- Use 2 mL (1 mL minimum) serum from a Red Top (No Additive) tube.
- Do not use SST gel barrier tubes.
- Ship refrigerated or frozen if transporting the specimen.
Doctor's Notes
Reviewed by Dr Ramarao Paidisetty — MBBS, MD (Biochemistry) · Reg. No. 21504
"Because phenytoin has a narrow therapeutic window, regular trough-level measurement helps balance seizure control with the risk of toxicity."
Last medically reviewed: September 7, 2026
Test Parameters & Specifications
Sample Stability
- SST gel barrier tube used
- Insufficient sample volume (less than 1 mL serum)
- Sample not collected at trough level
- Mislabeled or unlabeled specimen
Understanding Your Results
May be subtherapeutic; risk of inadequate seizure control. Clinical correlation needed.
Level: Below 10 mcg/mL
Usually considered therapeutic for most patients.
Level: 10-20 mcg/mL
May indicate toxicity; dose adjustment or clinical evaluation may be required.
Level: Above 20 mcg/mL
Consult your doctor if phenytoin level is outside the therapeutic range or if you develop symptoms such as nausea, vomiting, dizziness, confusion, slurred speech, difficulty walking, tremors, seizures, or blurred or double vision.
Limitations
- ⚠The test measures total phenytoin; free phenytoin may be more clinically relevant in certain conditions such as renal failure or hypoalbuminemia.
- ⚠Therapeutic ranges may vary depending on laboratory and individual patient factors.
- ⚠Results should be interpreted along with clinical history and examination.
Risks & Considerations
- ●Mild bruising at the needle site
- ●Bleeding
- ●Infection
- ●Dizziness or fainting
Interfering Factors
- ●Phenytoin exhibits dose-dependent pharmacokinetics; small dosage changes can cause large changes in serum levels.
- ●Concurrent use of drugs that induce or inhibit hepatic enzymes may alter phenytoin levels.
- ●Serum protein changes, such as hypoalbuminemia, may affect total phenytoin measurements.
- ●Timing of sample collection is critical; non-trough samples may overestimate steady-state levels.
Compare With Similar Tests
| Test | Phenytoin Test | ||
|---|---|---|---|
| Comparison | Phenytoin Test |
Frequently Asked Questions
What is the cost of the Phenytoin test at DNA Labs India?
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Is fasting required for the Phenytoin test?
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What is the therapeutic range of phenytoin?
What are the signs of phenytoin toxicity?
Is home sample collection available for the Phenytoin test?
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