CPT Code


Specimen Type


Container Type

Red-Clot Activator


Room Temperature, 2 days; 2-8°C, 1 month; -20°C, 5 months

Handling Instructions

Allow to clot for 30 minutes; centrifuge within 2 hours; transfer to pour off tube

Clinical Notes

Monitoring phenytoin concentrations, along with careful clinical assessment, is the most effective means of improving seizure control, reducing the risk of toxicity, and minimizing the need for additional anticonvulsant medication for the following reasons: Phenytoin concentrations correlate better with pharmacologic activity than does dosage because of individual differences in absorption, metabolism, disease states, concomitant medication, and compliance. Concentration monitoring helps physicians individualize dosage regimens.The hepatic enzyme system for metabolizing phenytoin can become saturated within the drug’s therapeutic range. When this occurs, small dosage alterations can lead to unexpected drug accumulation and clinical toxicity.Phenytoin is safe and effective only in a narrow range of concentrations.

Performing Lab

Principle Laboratory - Dallas
6210 N Belt Line Rd
Irving, TX 75063

Principle Laboratory - Houston
16840 Buccaneer Ln
Suite 281
Houston, TX 77058