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Complete Blood Count (CBC): What This Test Is and Why Your Doctor May Order It

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

This test measures the amount of barbiturate drugs in your blood to monitor treatment or check for poisoning.

Quick summary

{"Barbiturates are sedative medications used for sleep, seizure control, and anesthesia","The test checks if the drug level is in the therapeutic range or toxic","Blood is drawn from a vein in your arm for testing","Results help doctors adjust medication doses or diagnose overdose"}

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

Key facts at a glance

LOINC
43827-5
Short code
BARB
Synonyms
Barbiturates Spec-mCnc
Category
chemistry
Sample
serum
Container
Red-top serum tube (no anticoagulant) or serum separator tube (SST)
Units
N/A
Ref low
200
Ref high
300
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
Immunoassay (e.g., EMIT, FPIA) with confirmation by Gas Chromatography-Mass Spectrometry (GC-MS) or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
CPT
80345
SNOMED
441776005
Specimen volume
1-2 mL serum
Stability
Serum stable for 24 hours at room temperature (20-25°C), 7 days refrigerated (2-8°C), and up to 30 days frozen (-20°C or below)
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–72 hours
Order
routine

What is this test, and what does it measure in my body?

The barbiturate blood test measures the concentration of barbiturate drugs in your serum (the liquid part of your blood). Barbiturates are a class of prescription medications that act as central nervous system depressants. They are commonly used for conditions such as epilepsy, insomnia, and as pre-operative anesthesia. This test helps healthcare providers ensure the drug level is within the therapeutic range—not too low to be ineffective, and not too high to cause toxicity.

How is the test performed, and will I need to do anything to prepare for it?

A healthcare professional will draw a small blood sample from a vein in your arm using a needle. The sample will be sent to a laboratory for analysis. The test measures the mass of barbiturates per volume of serum. No special preparation is typically required, but follow your doctor's instructions regarding timing of the test relative to your medication dose.

Why might I need this test, and how will my doctor use the results?

Your doctor may order this test if you are taking barbiturate medications to monitor proper dosing, if you are experiencing symptoms that could be related to the medication, or if there is concern about overdose. It may also be used in emergency settings when a patient shows signs of drug poisoning or when monitoring patients on long-term barbiturate therapy.

Reference range

Negative (cutoff typically 200-300 ng/mL for screening; varies by laboratory and specific barbiturate)N/A

Specimen: serum

No fasting required. Patient should be informed that this test is used to detect barbiturate use or exposure. Clinical context including time of last dose and medication history should be provided.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is clinically significant for several reasons: (1) Therapeutic drug monitoring - ensuring barbiturate levels remain within the effective but safe range; (2) Toxicity assessment - detecting dangerously high levels that may cause respiratory depression, coma, or death; (3) Treatment compliance - verifying that patients are taking their medication as prescribed; (4) Differential diagnosis - helping distinguish barbiturate overdose from other causes of sedation or coma. Therapeutic ranges vary depending on the specific barbiturate and the condition being treated.

Frequently asked questions

How long does it take to get results?
Results are typically available within 1-3 days, depending on the laboratory. Your healthcare provider will contact you with the results.
Does the test require fasting?
Generally, no fasting is required for this test. However, follow any specific instructions given by your doctor, as timing of the blood draw relative to your last dose may be important.
What are the therapeutic and toxic ranges?
Therapeutic ranges vary by medication. For phenobarbital, the therapeutic range is typically 10-40 mcg/mL. Levels above 40 mcg/mL may cause toxicity. Toxicity can occur at different levels depending on individual tolerance and the specific barbiturate used.
What are the symptoms of barbiturate overdose?
Symptoms of overdose include excessive drowsiness, confusion, slurred speech, impaired coordination, slow breathing, and in severe cases, coma or death. Seek immediate medical attention if overdose is suspected.
  1. 1
    MedlinePlus - Barbiturate Screen and Confirmation (Blood)Source
  2. 2
    Mayo Clinic Laboratories - Barbiturates, SerumSource
  3. 3
    LOINC Code 43827-5Source

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