Lab Test

Phenobarbital Level

Luminal, Donnatal, Quadrinal, Phenobarbital Level, Serum

Test Codes

Antrim #15955, EPIC: LAB5409, SOFT: PHENO

Specimen Collection Criteria

Collect: One plain Red-top tube. (Minimum Whole Blood: 1.0 mL)

Do not use Serum Separator Tubes.
See Minimum Pediatric Specimen Requirements for Microtainer® collection.
Time of Collection: Trough, just prior to the next dose.
Record the exact time of specimen collection on the tube or in the computer system.

Physician Office/Draw Specimen Preparation

Let specimens clot 30-60 minutes and refrigerate (2-8°C or 36-46°F) the collection tube within two hours of collection. (Minimum: 1.0 mL blood)

Preparation for Courier Transport

Transport: Collection tube, refrigerated (2-8°C or 36-46°F). (Minimum: 1.0 mL blood)

Rejection Criteria

Serum Separator (SST) tubes.

Severely lipemic or hemolyzed specimens. 

In-Lab Processing

Let specimens clot 30-60 minutes. Centrifuge specimen to separate serum from cells. Deliver an aliqout of serum or the collection tube immediately to the appropriate testing station.


Specimen Stability for Testing:

Collection Tubes
Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 3 months

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days


Royal Oak Toxicology Laboratory


Sunday – Saturday, 24 hours a day.
STAT results available within 1 hour of receipt in the Laboratory.
Routine results available within 24 hours.

Reference Range

Therapeutic Range: 20-40 mcg/mL.
Critical Range: Greater than 50 mcg/mL.

Test Methodology

Particle Enhanced Turbidimetric Inhibition Immunoassay.


Barbiturates are sedatives and respiratory depressants. Serum concentrations above the critical level warrant prompt evaluation.

Clinical Utility

Phenobarbital is an anti-convulsant and sedative-hypnotic drug. It is used for the treatment of epilepsy, particularly for controlling focal motor or sensory seizures and grand mal seizures. It is frequently co-administered with phenytoin for the control of complex seizure disorders and with valproic acid for complex partial seizures.

Monitoring the serum concentrations of phenobarbital has been shown to improve patient therapy by aiding the physician in adjusting their dosage. Phenobarbital has a narrow therapeutic index and wide inter-individual variability in the rate of metabolism and clearance. This assay is used to monitor the therapeutic drug level and evaluate the toxicity of phenobarbital.

CPT Codes

80345 (alternate: G0480).


Last Updated


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This directory currently reflects information only for specimens collected and/or processed at the
Farmington Hills, Grosse Pointe, Royal Oak, and Troy campuses.