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Test 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, S

Specimen Type

Serum Red

Specimen Required

Container/Tube: Red top

Specimen Volume: 2 mL

Collection Instructions: Red-top tubes should be centrifuged and aliquoted 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


Mild OK; Gross reject






Serum gel tube


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) and Time(s) Performed

Monday through Sunday; Continuously

Performing Laboratory

Mayo Medical Laboratories in Rochester

LOINC Code Information

Test ID Test Order Name Order LOINC Value
PNTFT Phenytoin, Total and Free, S In Process


Result ID Test Result Name Result LOINC Value
PNYF Phenytoin, Free, S 3969-3
PNYA Phenytoin, Total, S 3968-5

CPT Code Information

Phenytoin, total-80185

Phenytoin, free-80186