Phenytoin, Free : 1000768

Test Code
PTNF or 1000768

Alias/See Also
Dilantin Free; Free Dilantin; Free Phenytoin; Phenytoin, Free

CPT Codes

Timing of specimen collection: Pre-dose (trough) draw - At steady state concentration.

Plain red.

Transport Container
Centrifuge plain red and aliquot serum from cells within 2 hours of collection. Transfer 2 mL serum into a standard transport tube. (Min: 1 mL)

Transport Temperature

Specimen Stability
After separation from cells: Ambient: 4 days; Refrigerated: 4 days; Frozen: 1 month

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Citrated plasma. Serum separator tubes (SST). Tubes that contain liquid anticoagulant.

Quantitative Enzyme Multiplied Immunoassay Technique

Setup Schedule
Tuesday - Saturday

Report Available
1-4 days (From receipt at performing laboratory)

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-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.

This test was developed and its performance characteristics determined by ARUP Laboratories. The U.S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.

Reference Range
Therapeutic: 1.0-2.5 ug/mL

Toxic: Greater than 2.5 ug/mL

Clinical Significance
Useful for therapeutic drug management for patients with renal failure or conditions that may alter albumin concentrations.

Performing Laboratory
ARUP Laboratories

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.