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HelpTest ID PNTFT Phenytoin, Total and Free, Serum
Useful For
Monitoring for appropriate therapeutic concentration of both free and total phenytoin: free phenytoin level is the best indicator of adequate therapy in renal failure
Specimen 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 Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum Red | Refrigerated (preferred) | 7 days |
| Frozen | 14 days | |
| Ambient | 7 days |
Reject Due To
| Gross hemolysis | Reject |
Reference Values
Phenytoin, Total
Therapeutic: 10.0-20.0 mcg/mL
Critical value: ≥30.0 mcg/mL
Phenytoin, Free
Therapeutic: 1.0-2.0 mcg/mL
Critical value: ≥2.5 mcg/mL
Day(s) Performed
Monday through Sunday
Report Available
Same day/1 dayPerforming Laboratory
Mayo Clinic Laboratories in Rochester
CPT Code Information
Phenytoin, total-80185
Phenytoin, free-80186
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.