Phenytoin Level


Abbrev Code:PHYT   
Order Code:LAB31Order Name:Phenytoin Level
Synonyms:Dilantin; Diphenylhydantoin; Fosphenytoin
Methodology:Turbidmetric rate
GH: Homogenous enzyme immunoassay
SJO/SJN: Chemiluminescent microparticle immunoassay (CMIA)
CPT Codes: 80185 x1
Turnaround Time:Performed and reported 24 hours/day.


Collection Instructions

Specimen:Blood
Optimal Volume:2.5 mL
Minimum\Peds Volume:0.6 mL
Container:Red (no gel), St Johns/St Joseph/Woodwinds-Green (lithium heparin, no gel)
Alternate Containers: St Johns/St Joseph/Woodwinds - Red (no gel)
Collection Instructions:Trough level is preferred; collect immediately before dose. It is advisable to monitor at the same time in the dosing schedule. Collect peak level 1.5-3 hours after solid dosage (rapid dissolution) formulation or 3-9 hours after extended dissolution.
Causes for Rejection:Collected in a gel tube, collected in a purple (EDTA) tube.
Contraindications:Fosphenytoin, a phosphate ester of phenytoin, cross-reacts with this assay. Samples from patients receiving fosphenytoin should be collected at least 2 hours following IV administration or 4 hours following IM administration. Phenytoin levels measured before complete conversion of fosphenytoin will not reflect phenytoin concentrations ultimately achieved. Fosphenytoin is measured as total phenytoin, Order PHYT with comment "Fosphenytoin".


Processing and Shipping

Specimen Processing:Centrifuge and transfer serum within 2 hours of collection. Aliquot 1.25 mL, 0.3 mL minimum. Store in refrigerator.
Shipping Instructions:Ship at refrigerated temperature.
Test Performed at or Referral Lab Chemistry  (Range, UMMC-East Bank, Lakes, Ridges, Southdale, UMMC/UMMCH-West Bank, Grand Itasca, St. Joseph's, St. John's)


Interpretive

Critical Range:Greater than 30 mg/L
Therapeutic Range:10-20 mg/L
Use:Monitor therapeutic dosing and evaluate toxicity. Half-life is 8-60 h.


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