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HelpTest Code 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
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| PNYF | Phenytoin, Free, S | Yes | Yes |
| PNYA | Phenytoin, Total, S | Yes | Yes |
Method Name
PNYF: Membrane Separation/KIMS
PNYA: Kinetic interaction of Microparticles in a Solution (KIMS)
Reporting Name
Phenytoin, Total and 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 |
|---|---|---|
| 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
Cautions
Toxicity is a constant possibility because of the manner in which phenytoin is metabolized. Small increases in dose can lead to very large increases in blood concentration, resulting in early signs of toxicity such as nystagmus, ataxia, and dysarthria. Severe toxicity occurs when the blood concentration is >30 mcg/mL and is typified by tremor, hyperreflexia, lethargy, and coma.
Day(s) Performed
Monday through Sunday
Report Available
Same day/1 dayPerforming Laboratory
Mayo Clinic Laboratories in Rochester
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| PNTFT | Phenytoin, Total and Free, S | 34540-5 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| PNYF | Phenytoin, Free, S | 3969-3 |
| PNYA | Phenytoin, Total, S | 3968-5 |
NY State Approved
YesCPT 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.