Phenytoin Lab Test

Dilantin, Epanutin, Eptoin
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    Clinical Definition of Phenytoin

    Phenytoin is an antiepileptic drug occassionally utilized in the treatment of some seizure disorders also known as epilepsy. Seizure conditions affect the brains ability to transmit electrical impulses and regulate nerve activity. Seizures are abnormal electrical discharges in the brain that temporarily distort the normal message transmission to the body. They produce alterations in consciousness, cause odd rhythmic or repetitive movements, jerking or twitching of limbs, and/or can lead to convulsions (a sudden uncontrollable attack) that contract muscles throughout the body. This test measures the amount of phenytoin in the blood. In the blood phenytoin is highly bound to serum proteins. The unbound or free is pharmacologically active. Phenytoin works by reducing the electrical conductance among brain cells, blocking excessive electrochemical activity occurring in the brain during a seizure. Phenytoin levels have to be observed as very low levels of phenytoin can lead to seizures in an affected person and high levels of phenytoin result in phenytoin toxicity.

    When do you expect results?

    24 to 36 Hours

    Why Get Tested?

    The phenytoin test diagnosis the phenytoin concentration in the blood, to maintain a therapeutic level, and to diagnose potential for toxicity. Phenytoin is utilized in seizures to control and treat them; that may begin during or after surgery to the brain or nervous system

    Reason to take Phenytoin Test

    Symptoms observed are:

    Slurred speech



    Low blood pressure

    Swelling of the gums and/or lymph nodes




    Difficulty swallowing



    changes in consciousness

    Alterations in sight, smell, and taste

    Uncontrolled muscular convulsions

    Loss of balance and falling

    Involuntary eye movement from side to side (nystagmus)

    Preparations Needed for Phenytoin Test

    Preparatory instructions before the test *:

    No Fasting Required.

    No other special preparations required.


    Sample Required?

    Specimen type: Serum (Blood Sample),

    Specimen collection procedure: Venipuncture Collection of blood from a vein, usually from the arm.

    Understanding results of Phenytoin

    Reference RangeInterpretation
    10 to 20 µg/mlTherapeutic range
    Above 20 µg/mlToxic range

    ‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’