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        Phenytoin

        Clinical Biochemistry

        Sample and container requirements

        Serum Lithium Heparin Plasma (paediatrics only)

        Minimum volume required

        Special requirements

        None

        Patient preparation

        Samples should be taken at trough drug levels by collecting a sample prior to the next dose.

        Sample viability

        Turnaround time

        2 days

        Reference range

        5 – 20 mg/L (Source: Pathology Harmony Recommendations)

        Clinical guidance

        Phenytoin is used to treat several seizure disorders (except absence seizures). It is also used as short-term prophylaxis after brain injury. Please refer to LabTestsOnlineUK to learn more about phenytoin. https://labtestsonline.org.uk/tests/phenytoin

        Notes

        Images to go here

        This information was last updated on 19 August 2026