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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Phenobarbital

Test Code(s): PENO / PHEN

CPT Code(s): 80184

Methodology: Particle Enhanced Turbidometric Inhibition Immunoassay (PETINIA)

Clinical Significance: Anticonvulsant, sedative

Days Performed: Daily, 24 hours.

Turnaround Time: Stat: 1 hour.
Routine: 4 hours.

Specimen Requirements

Specimen: Blood

Collection Instructions: Collect specimen within 30 minutes prior to the morning dose.

Collection Container: Preferred: Red top
Also Acceptable: Green top (with lithium heparin anticoagulant)

Collection Volume: Preferred: 2 mL
Pediatrics: 0.4 mL

Sample Analyzed: Serum or plasma

Volume Required: Preferred: 1 mL
Pediatrics: 0.2 mL

Specimen Processing: Centrifuge.  Transfer cell-free serum or plasma to plastic vial.  Refrigerate.

Specimen Transport: Transport specimen to UWHC Core Laboratory (B4/220). Transport with coolant pack if coming from outreach location.

Unacceptable Criteria: Specimens collected in red cap with yellow ring (SST) or green cap with yellow ring (PST)tubes are not acceptable.

Stability: Refrigerated: 7 days


Generally effective therapeutic concentration: 15-40 mcg/mL

Critical Calls: View

Additional Information:

Result of "BELOW" indicates that the level is below the instrument detection limit of 2.1 mcg/mL. The half-life is approximately 4 days. The average peak blood concentration following oral administration is approximately 4.5 hours. Concurrent administration with valproic acid may cause a marked increase in the phenobarbital concentration. It may require 14-21 days to achieve steady state. Phenobarbital is considered an hepatic enzyme inducer. It is not extensively protein bound and is both hepatically and renally eliminated.

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