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Test Code PHENX or LAB30 Phenobarbital Level, Serum or Plasma

Important Note

For information on draw times, please call Bronson lab client services at 269-341-6440.

For general guidelines on therapeutic drug monitoring (TDM), please see the TDM general guidelines document. 

Specimen Requirements

Container Type:

Optimal: Gold or Mint*

*For STAT requests

Acceptable: Red or Green
Optimal Collection Volume: 

4.5mL; full tube
Minimum Volume:
  • Adults: 1 mL whole blood
  • Neonates: 1 microtainer (400-600 uL)
Collection Instructions:

Gently invert the sample 5-6 times after collection.
Specimen Transport:

Refrigerate
Processing Instructions: 

1. If serum, allow the specimen to clot for 30 minutes.

2. Centrifuge specimen within 2 hours of collection.

3. After centrifugation, specimen tubes without a gel barrier should have the serum or plasma aliquoted to a false bottom container.

4. Keep the serum or plasma refrigerated until testing can be performed.

Specimen Stability

Specimen Type Temperature Time
Serum* Refrigerated 7 days
Room Temperature 7 days
Frozen 1 year

*Note: Heparinized plasma in gel separator tubes is less stable than serum and is only suitable for add-on testing up to 2 days following sample collection.

Specimen Rejection Criteria

Hemolysis Mild OK; Moderate OK; Gross Reject
Lipemia Mild OK; Moderate OK; Gross Reject
Icterus Mild OK; Moderate OK; Gross Reject
Other Quantity not sufficient

Useful For

Monitoring therapeutic concentrations of phenobarbital.

Methodology

Roche Cobas - Kinetic interaction of microparticles in solution (KIMS)

Reference Ranges

Therapeutic range: 15-40 ug/mL

 

Critical Value: > 60 ug/mL

Interpretive

In most patients, a therapeutic response is achieved with Phenobarbital concentrations in the 10-30 µg/ml range. Some patients may require serum or plasma levels outside this range to obtain effective seizure control due to patient-to-patient differences in metabolic activity. Values > 60 ug/ml are potentially toxic and should be immediately called to the physician or pharmacy.

Day(s) Performed

24/7

Expected TAT

Same day

Performing Laboratory

Bronson Laboratory, Chemistry - Kalamazoo

Sample Retention Time

7 days

CPT Code

80184

LOINC Code

3948-7