Sign in →

Test Code PRIMIDONE Primidone and Phenobarbital, Serum

Useful For

Assessing compliance


Monitoring for appropriate therapeutic levels of primidone and phenobarbital


Assessing toxicity

Profile Information

Test ID Reporting Name Available Separately Always Performed
PRIMD Primidone, S No Yes
PBR Phenobarbital, S Yes Yes

Testing Algorithm

Includes phenobarbital determination.

Method Name

PRIMD: Immunoassay

PBR: Kinetic Interaction of Microparticles in a Solution (KIMS)

Reporting Name

Primidone and Phenobarbital, S

Specimen Type


Specimen Required


Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL

Collection Instructions:

1. Serum gel tubes should be centrifuged within 2 hours of collection.

2. Red-top tubes should be centrifuged and aliquoted within 2 hours of collection.

Seattle Children's Hospital Note:

Collect 1.0 mL whole blood in a red or gold top.

Specimen Minimum Volume

0.25 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 7 days
  Frozen  28 days
  Ambient  72 hours

Reject Due To


Mild OK; Gross reject







Reference Values


Therapeutic: 5.0-12.0 mcg/mL

Critical value: ≥15.0 mcg/mL



Therapeutic: 10.0-40.0 mcg/mL

Critical value: ≥60.0 mcg/mL

Method Description


The assay is a homogeneous enzyme immunoassay technique used for the analysis of specific compounds in biological fluids. The assay is based on competition between drug in the sample and drug labeled with the enzyme glucose-6-phosphate dehydrogenase (G6PDH) for antibody binding sites. Enzyme activity decreases upon binding to the antibody, so the drug concentration in the sample can be measured in terms of enzyme activity. Active enzyme converts oxidized nicotinamide adenine dinucleotide (NAD) to NADH (the reduced form of NAD), resulting in an absorbance change that is measured spectrophotometrically. Endogenous serum G6PDH does not interfere, because the coenzyme functions only with the bacterial (leuconostoc mesenteroides) enzyme employed in the assay.(Package insert: Seimens Primidone reagent, Seimens Healthcare Diagnostics Ltd., Newark, DE)



The assay is based on the kinetic interaction of microparticles in a solution (KIMS). Phenobarbital antibody is covalently coupled to microparticles and the drug derivative is linked to a macromolecule. The kinetic interaction of microparticles in solutions is induced by binding of drug-conjugate to the antibody on the microparticles and is inhibited by the presence o fphenobarbital in the sample. A competitive reaction takes place between the drug conjugate and phenobarbital in the serum sample for binding to the phenobarbital antibody on the microparticles. The resulting kinetic interaction of microparticles is indirectly proportional to the amount of drug present in the sample.(Package insert: Roche Phenobarbital reagent, Roche Diagnostic Corp, Indianapolis, IN)

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information



LOINC Code Information

Result ID Test Result Name Result LOINC Value
PBR Phenobarbital, S 3948-7
PRIMD Primidone, S 3978-4