Phenytoin Level


Abbrev Code:PHYT   
Order Code:LAB31Order Name:Phenytoin Level
Synonyms:Dilantin; Diphenylhydantoin; Fosphenytoin
Methodology:Roche: Kinetic interaction of microparticles in a solution (KIMS)
Vista: Turbidmetric rate
GH Remisol: Homogenous enzyme immunoassay
Architect: Chemiluminescent microparticle immunoassay (CMIA)
CPT Codes: 80185 x1, 80185 x1
Turnaround Time:Performed and reported 24 hours/day.
Associated Links:

Roche Go Live Schedule



Collection Instructions

Specimen:Blood
Optimal Volume:2.5 mL
Minimum\Peds Volume:0.6 mL
Collection Instructions:Chemistry Tests Containers Chart

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.
Stability:Roche: 4 days at room temperature; 4 days refrigerated; 2 months frozen. 
Vista: 4 days at room temperature; 4 days refrigerated; 1 month frozen. 
Test Performed at or Referral Lab Chemistry  (Grand Itasca, Range, Roche-Lakes, Roche-Ridges, Roche-St. John's, Roche-UMMC East, Southdale, UMMC/UMMCH-West Bank)


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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