Allow sample to clot in an upright position for at least 60 minutes, then centrifuge sample and transfer serum to a plastic transport tube within 2 hours of collection. Clearly label tube as serum from a plain red top tube. Refrigerate.
Note: Ideal sampling time for all antiepileptic drugs is immediately before the next oral dose (trough). If this is not possible, patients should not be advised to delay their scheduled dose for longer than 2-3 hours. Sample collection and the time that the medication was last ingested should be noted on the requisition.