Laboratory Test Guide: What Patients Should Know
This test measures the amount of barbiturate medications in your blood to ensure safe and effective dosing.
{"Measures barbiturate drug levels in blood serum","Used to monitor patients taking barbiturates for seizures or sedation","Helps prevent drug toxicity and ensures therapeutic levels","Blood sample is typically drawn in the morning before taking medication","Results help doctors adjust dosage for optimal treatment"}
Key facts at a glance
- LOINC
- 4137-6
- Short code
- BARB
- Synonyms
- Barbiturates Dose
- Category
- chemistry
- Sample
- serum
- Container
- Red-top vacuum tube (no anticoagulant) or serum separator tube (SST)
- Units
- N/A
- Ref low
- 15
- Ref high
- 40
- Critical range
- — – 60 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Gas Chromatography-Mass Spectrometry (GC-MS) or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
- CPT
- 80345
- SNOMED
- 395112001
- Specimen volume
- 1-2 mL of serum
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 24–72 hours
- Order
- routine
What is this test? This is a laboratory test that helps your healthcare provider learn more about your health by analyzing a sample, most often blood or urine, in a medical laboratory. The results give important information that supports diagnosis, treatment decisions, and ongoing monitoring of your condition.
The Barbiturate Blood Level Test measures the concentration of barbiturate drugs in your blood serum. Barbiturates are a class of medications commonly used to control seizures, treat insomnia, or provide sedation during medical procedures. Examples include phenobarbital, pentobarbital, and secobarbital.
Why is this test performed? Your doctor may order this test to check how well your body is working, to help find the cause of symptoms you are experiencing, to confirm or rule out a suspected condition, or to monitor an illness you already have and see how well your current treatment is working over time.
This test is performed to monitor the level of barbiturate medication in your body. Maintaining the right concentration is crucial—too little may not effectively control seizures or provide sedation, while too much can lead to dangerous side effects or overdose. Regular monitoring helps your doctor ensure you are receiving the correct dose for your condition.
How is the test done? In most cases, a trained healthcare professional will collect a small sample of blood from a vein in your arm using a thin needle, a process that usually takes only a few minutes. You may feel a quick sting or pinch at the site. The sample is then sent to a laboratory for analysis, and results are typically available within a few days.
A healthcare professional will draw a blood sample from a vein in your arm. The sample is then sent to a laboratory for analysis. For accurate results, blood is typically collected in the morning before you take your daily dose of medication, as this provides a 'trough' level—the lowest concentration in your bloodstream.
What do the results mean? Your results will be compared with standard reference ranges to show whether your values are normal, high, or low. Abnormal results do not always mean you have a serious problem, so your healthcare provider will review them with you, explain what they mean in the context of your overall health, and discuss any follow-up testing or treatment if needed.
Results are reported as a concentration (mass) of barbiturate per volume of blood. Your doctor will interpret the results based on the specific barbiturate you are taking, your medical condition, and your individual response to the medication. Therapeutic drug monitoring helps maintain effective treatment while minimizing side effects.
Reference range
Therapeutic range varies by specific barbiturate: Phenobarbital 15-40 mcg/mL; Secobarbital 1-5 mcg/mL; Pentobarbital 1-5 mcg/mL; Amobarbital 1-5 mcg/mL. Toxic levels generally exceed 50 mcg/mL for phenobarbital and 10 mcg/mL for short-acting barbiturates.N/A
No fasting required. Specimen should be collected at trough level (just before next dose) for therapeutic monitoring. Document time of last dose on requisition. Avoid alcohol consumption prior to collection as it may potentiate barbiturate effects and alter metabolism.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The Barbiturate Blood Level Test is essential for patients receiving long-term barbiturate therapy for seizure disorders, such as epilepsy. It helps ensure therapeutic drug levels are maintained while preventing toxicity. Abnormal results may indicate the need for dose adjustment, poor medication adherence, drug interactions, or impaired liver function that affects drug metabolism. Regular monitoring is particularly important in children, pregnant patients, and elderly patients who may have altered drug clearance.
Frequently asked questions
Do I need to fast before this test?
How often do I need this test?
What are the side effects of barbiturates?
Can other medications affect test results?
Sources
- 1
- 2
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 15, 2026. · Read our editorial policy