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Phenytoin Level

Serum Phenytoin Diphenylhydantoin
Serum (SST) mg/L

About this test

Antiepileptic drug. Total and free (unbound) levels available; free level preferred with hypoalbuminaemia or uraemia.

Reference Ranges

Sex Age Range Notes
All ≥ 18 yrs 10 – 20 Total phenytoin; free phenytoin: 1–2 mg/L

Clinical Interpretation

Low / Decreased
Subtherapeutic — breakthrough seizures.
High / Increased
Toxicity — nystagmus, ataxia, dysarthria, CNS depression.

Related Tests

Albumin
Specimen
Serum (SST)
Reporting Unit
mg/L
Category
🧪 Clinical Biochemistry

⚠ Clinical Note
Reference ranges are indicative. Always interpret results in the context of the individual patient and local laboratory reference intervals, which may vary.