Ordering Recommendation

Therapeutic drug management for patients with renal failure or conditions that may alter albumin concentrations.

Mnemonic

DIL FR

Methodology

Quantitative Enzyme Multiplied Immunoassay Technique

Performed

Sun-Sat

Reported

1-4 days

New York DOH Approval Status

This test is New York DOH approved.

Specimen Required

Patient Preparation

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

Collect

Plain red.

Specimen Preparation

Separate serum from cells within 2 hours of collection. Transfer 2 mL serum to an ARUP Standard Transport Tube. (Min: 1 mL)

Storage/Transport Temperature

Refrigerated.

Unacceptable Conditions

Citrated plasma. Serum separator tubes (SST). Tubes that contain liquid anticoagulant.

Remarks
Stability

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

Reference Interval

Effective May 16, 2016

Therapeutic: 1.0-2.5 µg/mL
Toxic: Greater than 2.5 µg/mL

Interpretive Data

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.

Compliance Category

FDA

Note

Hotline History

N/A

CPT Codes

80186

Components

Component Test Code* Component Chart Name LOINC
2010493 Phenytoin - Free 3969-3
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.

Aliases

Phenytoin, Free