| Ordering Code | 5454 |
|---|---|
| Test Name | Phenytoin/Free Phenytoin |
| Alias | Free Dilantin Free Phenytoin Dilantin/Free Dilantin |
| Preferred Specimen | Plasma |
| Preferred Container | Lithium Heparin PST (Green) |
| Other Specimen/Container | Plasma in Lithium Heparin (Dark Green-PP No Gel), Plasma in K2 EDTA (Lavender), Serum in SST (Gold), Serum in Plain (Red) |
| Optimum Volume | 2 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. |
| 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 (Aliquot) |
| Specimen Stability | Refrigerated: 24 Hours (Centrifuged, unaliquoted gel separator tubes), 1 Month (Aliquot) Frozen: 3 Months (Aliquot) Frozen samples should be thawed only once. |
| Rejection Criteria | Grossly hemolyzed, Insufficient quantity, Specimen older than stability limits, Uncentrifuged gel separator tube specimens >2 hours old, Unaliquoted gel separator tube specimens >24 hours old |
| 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 February 21, 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 | |||
| Free Phenytoin | ALL | 1.0-2.0 | >= 2.5 | 1.0-2.0 | >= 2.5 | ug/mL |