Phenytoin Level
| Abbrev Code: | PHYT | ||
| Order Code: | LAB31 | Order Name: | Phenytoin Level |
| Synonyms: | Dilantin; Diphenylhydantoin; Fosphenytoin | ||
| Methodology: | Roche: Kinetic interaction of microparticles in a solution (KIMS)
Vista: Turbidmetric rate Architect: Chemiluminescent microparticle immunoassay (CMIA) |
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| CPT Codes: | 80185 x1, 80185 x1 | ||
| Turnaround Time: | Performed and reported 24 hours/day. | ||
| Associated Links: | |||
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. |
| 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 (Roche-Grand Itasca, Roche-Lakes, Roche-Northland, Roche-Range, Roche-Ridges, Roche-Southdale, Roche-St. John's, Roche-UMMC East, 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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