Lab Test

Primidone (including Phenobarbital)


Test Codes


Specimen Collection Criteria

Collect: One plain Red-top tube. (Minimum:2.0 mL blood).

Do not use Serum Separator Tubes.
Time of Collection: Trough, just prior to the next dose.

Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes. Refrigerate (2-8°C or 36-46°F) the colletion tube within two hours of collection. (Minimum: 2.0 mL bood).

Preparation for Courier Transport

Transport: Collection tube, refrigerated (2-8°C or 36-46°F). (Minimum: 2.0 mL blood)

Rejection Criteria

  • Serum Separator (SST) tubes.
  • Severly lipemic or hemolyzed specimens.

In-Lab Processing

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


Specimen Stability for Testing:

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:

Frozen (-20°C/-4°F or below): 2 months


Royal Oak Toxicology Laboratory


Sunday – Saturday.
Results available the same day as testing performed.

Reference Range

Primidone: 5.0-12.0 mcg/mL.
Phenobarbital: 20.0-40.0 mcg/mL.

Test Methodology

Primidone: High Performance Liquid Chromatography/Tandem Mass Spectrometry (LC-MS/MS).
Phenobarbital: Particle Enhanced Turbidimetric Inhibition Immunoassay.

This test was developed and its performance characteristics determined by Beaumont Health. It has not been cleared or approved by the FDA. The Laboratory is regulated under CLIA as qualified to perform high-complexity testing. This test is used for clinical purposes and should not be regarded as investigational or for research.


  • Primidone concentrations greater than 15 mcg/mL in conjunction with therapeutic levels of phenobarbital may be associated with toxicity.
  • Primidone is metabolized to phenobarbital and the serum concentrations of both substances are necessary to assess the therapeutic or toxic effect. Phenobarbital will increase the metabolism of other drugs and may necessitate dosage adjustments.

Clinical Utility

This assay is used to monitor the therapeutic drug levels and evaluate the toxicity of primidone and phenobarbital. Primidone is an anticonvulsant used to control grand mal seizures that are refractory to other anticonvulsant therapy and seizures of psychomotor or focal origin.

CPT Codes

80188, 80184.


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.