Phenytoin, Free

Abbrev Code:PHYFR   
Order Code:LAB5845Order Name:Percent free phenytoin panel
Synonyms:Free Dilantin; Unbound Phenytoin; PHYFER
Methodology:Quantitative enzyme multiplied immunoassay technique
CPT Codes: 80186 x1, 80186 x1
Turnaround Time:Routine specimens are sent to the reference laboratory Sun-Sat; results are reported within 1-4 days.

This test uses an in vitro diagnostic (IVD) that has been cleared or approved by the FDA.

Collection Instructions

Optimal Volume:4 mL
Minimum\Peds Volume:2.2 mL
Container:Red (no gel)
Collection Instructions:Timing of specimen collection: Pre-dose (trough) draw - At steady state concentration.
Causes for Rejection:Citrated plasma. Serum separator tubes (SST). Tubes that contain liquid anticoagulant.

Processing and Shipping

Specimen Processing:Centrifuge and aliquot 2 mL,1 mL minimum; minimum volume does not permit repeat analysis. Store in refrigerator.
Shipping Instructions:Ship at refrigerated temperature. If 4 days or greater, ship on dry ice.
Stability:After separation from cells: 4 days at room temperature or refrigerated; 1 month frozen.
Test Performed at or Referral Lab Lab Sendouts  (ARUP)
Referral Lab number:2010481


Critical Range:Toxic: Greater than 2.5 μg/mL
Therapeutic Range:1.0 - 2.5 μg/mL
Use:Therapeutic drug management for patients with renal failure or conditions that may alter albumin concentrations.

Free phenytoin may be important to monitor in patients with altered or unpredictable protein binding capacity because phenytoin is highly bound (greater than 90 percent) at therapeutic concentrations. Phenytoin is also subject to drug interactions due to displacement of protein binding and extensive metabolism. Cross-reactivity with metabolites may account for differences in phenytoin concentrations among analytical methods.

Click HERE to Report test errors or omissions.
*If no email program is associated with this computer, please contact: for TestID: 3506"