| Ordering Code | 440 |
|---|---|
| Test Name | Phenytoin |
| Alias | Dilantin-125 Phenytek Diphenyldantoin Infatabs PHENY Phenytoin Dilantin |
| Preferred Specimen | Plasma |
| Preferred Container | Lithium Heparin PST (Green) |
| Other Specimen/Container | Plasma in EDTA, K2 (Lavender), Serum in Plain (Red), Serum in SST (Gold) |
| Optimum Volume | 1 mL |
| Collection Instructions | Blood samples for phenytoin should be collected within two to four hours after an intravenous loading dose. At a steady state, collect a sample representing a trough level just before the next scheduled dose initiation and ajust as needed Long-term - stable patients: Monitor levels every 3 to 12 months. |
| Handling Instructions | All specimen types must be centrifuged within 2 hours of collection. If no gel separation present in tube and testing is delayed, plasma/serum is aliquoted from cells within 2 hours of collection Send aliquot if transport time >24 hours. |
| Transport Requirements | Oahu: Refrigerated Airline: Refrigerated Send frozen aliquot if transport time >4 days. |
| Specimen Stability | Refrigerated: 24 Hours (Centrifuged, unaliquoted gel separator tubes), 1 Month (Aliquot) Frozen: 3 Months (Aliquot) Frozen samples should be thawed only once be added to >24 hours, unaliquoted specimens Do not freeze Lithium Heparin Plasma. |
| Rejection Criteria | Grossly hemolyzed, Specimen older than stability limits, Uncentrifuged gel separator tube specimens >2 hours old, Unaliquoted gel separator tube specimens >24 hours old, Insufficient quantity |
| Avail. Stat | YES |
| Analytic Time | 1 Day |
| Methodology | Homogenous Enzyme Immunoassay (EMIT) |
Reference range(s)
The reference ranges listed below are valid on this date of March 12, 2026.
| Component | Age | Male Norm | Male Critical Low | Male Critical High | Female Norm | Female Critical High | Female Critical Low | Units | Add'l info |
|---|---|---|---|---|---|---|---|---|---|
| Phenytoin | ALL | 10.0-20.0 | >= 30.0 | 10.0-20.0 | >= 30.0 | ug/mL |