One 5 mL red top tube preferred. Also acceptable: One 4 mL green top tube (heparin) or one 4 mL lavender top tube (EDTA). Serum separator tube (SST) or gel barrier tubes may decrease phenytoin level from 16-22% in 24 hours and are not recommended.
Must be centrifuged within 2 hours, the serum or plasma separated from cells and poured into a plastic vial for transport. Refrigerate. Freeze if specimen cannot be assayed within 48 hours. Allow no more than one freeze/thaw cycle. Note date and time of last dose.
48 hours refrigerated.
0.5 mL serum or plasma.
150 µL serum or plasma.
Refrigerated, or frozen on dry ice.
Refer to the drug manufacturer’s package insert or the Physicians’ Desk Reference for proper dosage and for phenytoin measurement sampling times.
Specimen frozen and thawed more than once; refrigerated specimen received in laboratory more than 48 hours after collection.