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Epic Test Code LAB30 Phenobarbital

Performing Location(s)

BMC

Synonyms

Luminal, Phenobarb

Specimen Type

Serum 

Preferred Container

Red top tube

Blood Tube Draw Volume

Min 50% draw volume  

Minimum Volume to Submit for Testing

0.5 mL Serum 

  • Multiple test can be performed from this volume. For question please contact the lab at 547-3975.  

Transportation Needs

Deliver specimen to laboratory within 1 hour of collection if unspun. If not possible see "storage Requirements". 

Storage Requirements

Sample tubes should be centrifuged within 2 hours of collection followed by transfer of the serum to a labeled plastic, aliquot tube.

For long term storage, samples may be frozen for up to 3 months

Causes for Rejection

Mislabeled or Unlabeled specimen
Less than 50% draw for Vacutainer tubes

Drawn in anything other than a red top tube
Hemolysis >800 mg/dL HgB
Lipemia >750 mg/dL Trig
Bilirubin >30 mg/dL Bili
>30 days refrigerated (Serum tubes are routinely stored at the lab for only 7 days therefore, an add-on may not be possible after  days.) 
> 24 hours room temperature
> 3 months frozen 
 

Limitations

Although amobarbital does not interfere in the therapeutic range, a toxic level at 100 µg/mL [440µmol/L] amobarbital will increase the response of phenobarbital at a concentration of 30 µg/mL [130 µmol/L] by 22.0 µg/mL [95.3 µmol/L] units.

Reference Values

Population Units Therapeutic Range High Critical Value
General ug/mL 15-40 > 40.0

 

Days of Analysis

All

Available STAT

Yes

Additional Information

Additional Information:

Because of considerable inter-individual variation and the limited capacity for the liver to metabolize phenobarbital, blood concentrations should be monitored to obtain maximal anti-seizure effect. Once metabolism is saturated, small dosage changes may result in disproportionate changes in blood concentration and can cause wide variations in dosage requirements among patients.

 

Mephobarbital is rapidly metabolized in vivo to phenobarbital, its active metabolite

 

Collection Guideline:

Collect after steady state conditions are reached, i.e. after 4-5 half-lives on unchanged dose regimen.

 

Collect samples following oral dosing immediately prior to next dose for drugs with short half lives. For drugs with long half-lives, ≥24 hours, draw time is less critical.

 

Obtain samples following IV dosing of phenytoin at 1-4 hours post dose.

 

After administration of fosphenytoin, collect specimens 2 hours post IV or 4 hours post IM dose.
 

Collect within 6 hours after a seizure in previously controlled patient.

Methodology

Beckman AU/Dx Series

CPT Code

80184

Last Updated

19-DEC-24 MS