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HelpTest Code Billings Clinic: 8300 Mayo: PNTFT Phenytoin, Total and Free, Serum
Reporting Name
Phenytoin, Total and Free, SPerforming Laboratory
Mayo Clinic Laboratories in Rochester
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
Method Name
PNYF: Membrane Separation/KIMS
PNYA: Kinetic interaction of Microparticles in a 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
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
Interpretation
Dose should be adjusted to achieve steady-state concentrations of total phenytoin between 10.0 and 20.0 mcg/mL, and free phenytoin between 1.0 and 2.0 mcg/mL. The range for percent free phenytoin is 8% to 14%. However, response and side effects will be individual.
In patients with renal failure, total phenytoin is likely to be less than the therapeutic range of 10.0 to 20.0 mcg/mL. Severe toxicity occurs when the total blood concentration exceeds 30.0 mcg/mL.
Day(s) Performed
Monday through Sunday
Report 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
Phenytoin, total-80185
Phenytoin, free-80186
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 |
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.
Profile Information
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| PNYF | Phenytoin, Free, S | Yes | Yes |
| PNYA | Phenytoin, Total, S | Yes | Yes |