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Phenytoin, Free
2010481
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
Tue-Sat
Reported
1-4 days
New York DOH Approval Status
This test is New York DOH approved.
Submit With Order
ARUP Consult®
Disease Topics
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 Statement B: 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.

Note
CPT Code(s)
80186
Components
Component Test Code*Component Chart NameLOINC
2010493Phenytoin - Free3969-3
* 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