ARUP's Laboratory Test Directory

Phenytoin : 0090090

Mnemonic: DIL

Methodology: Enzyme Immunoassay
Performed: Sun-Sat
Reported: Within 24 hours
Specimen Required: Collect: Plain red.

Specimen Preparation: Allow serum specimen to clot completely at room temperature to ensure complete clot formation has taken place prior to centrifugation. Separate serum from cells ASAP or within 2 hours of collection. For plasma specimens, ensure centrifugation is adequate to remove platelets. Transfer 1 mL serum to an ARUP Standard Transport Tube. (Min: 0.2 mL)

Storage/Transport Temperature: Refrigerated.

Unacceptable Conditions: Specimens collected in separator tubes, sodium fluoride, potassium oxalate, EDTA tubes. Hemolyzed specimens.

Stability (collection to initiation of testing): After separation from cells: Ambient: 8 hours; Refrigerated: 4 days; Frozen: 1 month
Reference Interval:
0-2 months: 6.0-14.0 µg/mL
  Toxic: 14.1 µg/mL  or greater 
3 months and older: 10.0-20.0 µg/mL
  Toxic: 30.1 µg/mL or greater 
Interpretive Data: The therapeutic range for phenytoin applies to non-uremic patients. In critically ill uremic patients who are receiving fosphenytoin, the value reported may be higher than the patient's actual serum concentration due to interfering substances.
CPT Code(s): 80185
Cross References: Dilantin (Phenytoin), Phenytoin, Total, Serum (Phenytoin)