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HelpTest Code PNYF Phenytoin, Free, Serum
Additional Codes
CNE Order Code: Phenytn F
Useful For
Monitoring for appropriate therapeutic concentration of free phenytoin: free phenytoin level is the best indicator of adequate therapy in renal failure
Assessing compliance and toxicity
Method Name
Membrane Separation/Kinetic Interaction Microparticles in Solution (KIMS)
Reporting Name
Phenytoin, Free, SSpecimen Type
Serum RedSpecimen Required
Collection Container/Tube: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 2 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial within 2 hours of collection.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum Red | Refrigerated (preferred) | 7 days | |
| Frozen | 14 days | ||
| Ambient | 7 days |
Reject Due To
| Gross hemolysis | Reject |
Reference Values
Therapeutic: 1.0-2.0 mcg/mL Critical value: ≥2.5 mcg/mLInterpretation
Dose should be adjusted to achieve steady-state blood concentration of free phenytoin between 1.0 and 2.0 mcg/mL. The range for percent free phenytoin is 8% to 14%.
Severe toxicity occurs when the free phenytoin concentration is ≥2.5 mcg/mL. However, response and side effects will be individual.
Day(s) Performed
Monday through SundayReport Available
Same day/1 dayPerforming Laboratory
Mayo Clinic Laboratories in Rochester
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| PNYF | Phenytoin, Free, S | 3969-3 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| PNYF | Phenytoin, Free, S | 3969-3 |
CPT Code Information
80186
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.