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Pharmacokinetic profile of phenobarbital (serum concentration measurement)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of phenobarbital, a medication used to control seizures, in your blood. It helps doctors monitor your drug levels to ensure they’re effective and safe.

Quick summary

["This test helps adjust your phenobarbital dose for optimal seizure control and safety."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
54056-7
Short code
HEDIS 2009-11 MPM-E PHENobarbital
Synonyms
HEDIS 2009-11 MPM-E PHENobarbital
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order this test if you’re taking phenobarbital to manage seizures. It helps track how well your body is processing the medication and whether your current dose is working as intended.

What Does the Test Involve?

A blood sample is taken from a vein in your arm. The sample is then analyzed to measure the concentration of phenobarbital in your serum.

What to Expect Before the Test

No special preparation is usually needed, but inform your doctor about any other medications you’re taking, as they may affect test results or your dose.

What to Expect After the Test

You may feel slight discomfort or bruising at the injection site, but the area should heal quickly. Avoid heavy lifting or strenuous activity for a few hours afterward.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Phenobarbital levels are critical for managing epilepsy. Too little may not control seizures effectively, while too much can lead to side effects like drowsiness, confusion, or respiratory issues. This test helps balance your dose for safety and efficacy.

Short name

Phenobarbital Serum Level

Frequently asked questions

Why was this test ordered?
Your doctor may have ordered this test to check if your phenobarbital levels are within the target range for your condition, adjust your dose, or monitor for potential side effects.
What do the results mean?
Results are typically discussed with your healthcare provider, who will interpret them in relation to your medical history and symptoms. They’ll help determine if your dose needs to be changed or if other adjustments are needed.
Can I eat or drink before the test?
You can usually eat and drink normally before this test unless your doctor specifies otherwise. Avoid alcohol or caffeine in excess, as they may affect your medication levels.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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