CPT® Code 80186

The CPT® Code 80186 refers to the measurement of free phenytoin levels in the blood. Phenytoin, commonly known by its brand names such as Dilantin, Phenytek, or Phenytoin Prompt, is an anticonvulsant medication primarily used to manage and treat seizures. It functions by reducing electrical activity in the brain, which is crucial for preventing seizure episodes. The administration of phenytoin can occur either orally or through injection, depending on the clinical scenario and patient needs. Due to its narrow therapeutic range, it is essential to monitor both total and free phenytoin levels in patients receiving this medication. Total phenytoin levels indicate the overall serum concentration of the drug, while free phenytoin levels represent the unbound, biologically active portion of the drug. It is important to note that only the free phenytoin is pharmacologically active, as approximately 90% of phenytoin in the bloodstream is bound to proteins and thus inactive. This binding can be influenced by other medications that may displace phenytoin from its protein binding sites, potentially leading to elevated free phenytoin levels. Regular monitoring of blood concentration levels is critical, particularly during routine follow-ups and in instances of breakthrough seizures, which may suggest that the therapeutic levels of phenytoin are insufficient. The process of obtaining a blood sample for this test involves a venipuncture, which is reported separately, followed by the analysis of the serum using immunoassay techniques to determine the free phenytoin concentration.