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Test Code PTN Phenytoin (Dilantin) LAB31

Test Method

Turbidimetric Inhibition Immunoassay; Beckman DXC600

Specimen Requirement

0.5 mL serum or plasma is required.

Additional Specimen Collection Information

Collect blood in a lithium heparin, green-top or
red-top tube. Serum and plasma gel tubes are not acceptable. Peak
specimens should be collected at least 6 hours after last
dose. Trough level is collected just prior to next dose. Serum or
plasma should be separated from contact with the cells within 2
hours of collection. Specimens not centrifuged within 4 hours of
collection may be rejected. Refrigerate the specimen if unable
to assay within 8 hours of collection. Samples with >4+ lipemia
must be cleared prior to analysis.

Reference Values

10.0-20.0 mcg/mL

  • Toxic Level:  > 25 mcg/mL


Testing is performed Monday through Sunday.

Routine: Typically completed within 4 hours after the
specimen arrives at the testing site.

Expedite: Typically completed within 1 hour after the
specimen arrives at the testing site.

STAT: Typically completed within 30 minutes after the specimen
arrives at the testing site.

Useful For

Monitoring for appropriate therapeutic concentration

Assessing compliance or toxicity

LOINC Code Information

3968-5 Phenytoin [Mass/Volume] In Serum Or Plasma

CPT Code Information

80185 Therapeutic Drug Levels: Phenytoin