ARUP's Laboratory Test Directory
| 0090141: Phenytoin, Free & Total |
| Test Mnemonic: FDIL | |
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#ExistMethodology>
Methodology: Immunoassay
*ExistMethodology> #ExistPerformed> Performed: Sun-Sat *ExistPerformed> #ExistReported> Reported: 1-2 days *ExistReported> |
| Specimen Required: | |
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#ExistCollect>
Collect: One 5 mL plain red.
*ExistCollect> #ExistTransport> Transport: 2 mL serum at 2-8°C. (Min: 1 mL) Submit specimen in an ARUP Standard Transport Tube. *ExistTransport> #ExistPedCollectTransport> Pediatric Collection/Transport: 1 mL serum at 2-8°C. *ExistPedCollectTransport> #ExistRemarks> Remarks: Separate serum from cells ASAP. Avoid use of separator tubes and gels. *ExistRemarks> #ExistStability> Stability: After separation from cells: Ambient: 4 days; Refrigerated: 4 days; Frozen: 1 month *ExistStability> |
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| Reference Interval: | ||||||||||||
#ExistRefRange> Therapeutic Range:
*ExistRefRange>
#ExistRefRangeTable>
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| Interpretive Data: | |
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#ExistInterpData>
Free phenytoin may be important to monitor in patients with altered or unpredictable protein binding capacity because phenytoin is highly bound (greater than 90%) at therapeutic concentrations. Phenytoin is also subject to drug-drug interactions due to displacement of protein binding and extensive metabolism. Cross-reactivity with metabolites may account for differences in phenytoin concentrations among analytical methods. Calculating percent free attempts to minimize differences in assay cross-reactivity and may be useful in dose optimization.
*ExistInterpData> |
| CPT Code(s): | |
| 80185 Phenytoin, total; 80186 Phenytoin, free |