Phenobarbitone Test
Short Name: Phenobarbitone
Also known as: Phenobarbital Test, Phenobarbitone Level, PB Level, Barbiturate Level
Phenobarbitone Test test available at DNA Labs India for ₹1,076. Uses Chemiluminescent Immunoassay on Serum samples. Results in Reports are generally ready on the same day after sample collection.. Free home collection in 300+ cities across India.
🩺 Medically Reviewed By
Dr Ramarao Paidisetty
Consultant Biochemist · Reg: 21504
Last reviewed: September 7, 2026
Overview
The primary purpose of the Phenobarbitone test is to measure the amount of phenobarbitone in the blood to confirm that the drug concentration is within a safe and effective range. The test is also used to assess patient compliance, guide dose adjustment, and identify toxicity.
- Test Code
- 3542
- Price
- ₹1,076
- Sample Type
- Serum
- Result Time
- Reports are generally ready on the same day after sample collection.
- Fasting Required
- No
- Method
- Chemiluminescent Immunoassay
Sample Collection
Inform your doctor about your current dose, time of last dose, and all other medicines. The blood sample should ideally be collected just before the next scheduled dose after the drug has reached steady state.
Method: Peripheral venous blood collection
Laboratory Analysis
A trained phlebotomist will draw a small amount of blood from a vein in your arm. The procedure is quick and generally well tolerated.
Report Delivery
You can continue normal daily activities immediately after sample collection. If there is bleeding, apply pressure to the site.
Timeline: Reports are generally ready on the same day after sample collection.
Patient Instructions
About This Test
Who Should Get This Test
The primary purpose of the Phenobarbitone test is to measure the amount of phenobarbitone in the blood to confirm that the drug concentration is within a safe and effective range. The test is also used to assess patient compliance, guide dose adjustment, and identify toxicity.
How to Prepare
- Collect the sample immediately before the next phenobarbitone dose is due at steady state.
- Use a plain Red Top tube without additive. Avoid SST gel barrier tubes.
- Transport the sample refrigerated or frozen as per laboratory requirements.
Doctor's Notes
Reviewed by Dr Ramarao Paidisetty — MBBS, MD (Biochemistry) · Reg. No. 21504
"For phenobarbitone, the therapeutic window is narrow. A trough level should be interpreted with seizure response, side effects, and co-administered medicines. A single serum value is an aid, not an absolute target."
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 received refrigerated or frozen when transport was required
- Incomplete clinical or dose information on the request form
Understanding Your Results
May be subtherapeutic. The doctor may consider a dose increase if seizures are uncontrolled, though some patients are controlled at lower levels.
Range: Below 15 mg/L
Usual therapeutic reference range for phenobarbitone. Individual target may vary.
Range: 15–40 mg/L
Possible toxicity. Common signs include drowsiness, ataxia, confusion and respiratory depression.
Range: Above 40 mg/L
Seek medical attention if you develop severe drowsiness, confusion, shallow breathing, slow heart rate, unsteadiness, or any features of phenobarbitone overdose. Also consult your doctor if the test result is outside the therapeutic range.
Limitations
- ⚠Reference ranges are guidelines and may differ across laboratories
- ⚠Interpretation should include clinical context, dose history and comorbidities
- ⚠Immunoassay methods may show cross-reactivity with other barbiturates
Risks & Considerations
- ●Slight pain or discomfort during blood draw
- ●Mild bruising at the puncture site
- ●Dizziness or lightheadedness
- ●Rare risk of infection
Interfering Factors
- ●Sample collection not timed just before the next dose
- ●Concurrent use of other antiepileptic drugs that may alter phenobarbitone metabolism
- ●Use of SST gel barrier tubes, which is not recommended for this test
- ●Hepatic or renal dysfunction may affect drug clearance
Frequently Asked Questions
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