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HelpTest Code LAB31 Phenytoin (Dilantin)
Useful For
Anti-epileptic drug monitoring
Methodology
Kinetic interaction of microparticles in a solution (KIMS)
Performing Laboratory
Bozeman Health Laboratory Services
Specimen Requirements
Specimen Type: Plasma or serum
Container/Tube: Light-green top (lithium heparin gel), red top, or gold top
Specimen Volume: 1 mL
Specimen Minimum Volume: 0.5 mL
Collection Instructions:
- Keep specimen capped for stability. Spin down within 2 hours of draw.
- Serum phenytoin measurements should be collected at least 2 hours after an intravenous dose of fosphenytoin and at least 4 hours after an intramuscular dose.
Additional Information
- Serum for an oral trough level is usually drawn immediately prior to subsequent dose, 1 week after initiating therapy, and again 3 to 5 weeks later.
Specimen Transport Temperature
Ambient/Refrigerated
Specimen Stability
| Specimen Type | Temperature | Time |
|---|---|---|
| Plasma or Serum (capped) | Ambient | 4 days |
| Refrigerated | 4 days |
Reference Values
Therapeutic concentration: 10.0-20.0 µg/mL
Toxic concentration (automatic call-back): >30.0 µg/mL
Therapeutic phenytoin concentrations vary significantly depending on the individual patient. A range of 10.0 µg/mL to 20.0 µg/mL (39.6-79.2 µmol/L) for peak drug levels indicates effective plasma or serum levels for many patients; however, some individuals are best treated at concentrations outside this range. Concentrations >30.0 µg/mL (118.9 µmol/L) are often associated with toxic symptoms.
Day(s) Test Set Up
Monday through Sunday
Test Classification and CPT Coding
80185