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HelpTest Code PNYF Phenytoin, Free, Serum
Reporting Name
Phenytoin, Free, SPerforming Laboratory
Mayo Clinic Laboratories in Rochester
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)
Specimen 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 Type
Serum RedSpecimen 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 dayTest Classification
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.CPT Code Information
80186
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 |
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.