Phenytoin Level
| Abbrev Code: | PHYT | ||
| Order Code: | LAB31 | Order Name: | Phenytoin Level |
| Synonyms: | Dilantin; Diphenylhydantoin; Fosphenytoin | ||
| Methodology: | Turbidmetric rate
GH: Homogenous enzyme immunoassay SJO/SJN: Chemiluminescent microparticle immunoassay (CMIA) |
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| 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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