Fosphenytoin is ProDrug of Phenytoin and is measured as Phenytoin

Gold serum separator (SST) tube

• Specimen should be collected:
  • Peak (regular release): 1-3 hours post dose
  • Peak (slow release): 4-12 hours post dose
  • Trough: Immediately prior to next dose
• Immediately following collection, thoroughly mix sample by gently inverting 5 times

1. Allow sample to clot for a minimum of 30 minutes
2. Spin within two (2) hours of sample collection

Gold serum separator (SST) tube

Lt green plasma separator (PST)

Immediately following collection, mix sample thoroughly by gently inverting 8 - 10 times to prevent clotting

Spin within two (2) hours of sample collection

Lt green plasma separator (PST)

Refrigerated (preferred) - 4 days

Ambient - 4 days

Frozen - 2 months

• Improper labels (unlabeled or mislabeled)
• Hemolysis (some procedures)
• Improper anticoagulant or ratio
• Delay in transport
• Improper storage temperature affecting results
• Inappropriate timing of collection
• Improper container
• Leaking container resulting in compromised specimen
• Quantity not sufficient (QNS)

Kinetic interaction of microparticles in a solution (KIMS)

1.0 - 2.5 µg/mL

> 3.0 µg/mL

 If total phenytoin is >30 µg/mL, no call