{"id":"phenytoin","name":"Phenytoin (Total)","shortName":"Phenytoin","aliases":["Phenytoin","Dilantin","Phenytoin Level","Phenytoin, Serum","Dilantin Level","Phenytoin, Total","Total Phenytoin","Phenytoin Total Level","Diphenylhydantoin"],"abbreviations":["PHT"],"loinc":[{"code":"3968-5","primary":true},{"code":"14877-5","primary":false},{"code":"74976-2","primary":false},{"code":"97193-7","primary":false}],"specimen":"serum-or-plasma","units":[{"ucum":"ug/mL","display":"mcg/mL"},{"ucum":"mg/L","display":"mg/L"},{"ucum":"umol/L","display":"µmol/L"}],"referenceRanges":[{"population":"Adults","low":10,"high":20,"unit":"ug/mL","unitDisplay":"mcg/mL","note":"Therapeutic range for total phenytoin in people taking it, not a healthy-population interval. FDA labeling says seizure control without signs of toxicity is more likely at 10 to 20 mcg/mL (unbound 1 to 2 mcg/mL), although some people are controlled at lower levels. ARUP prints the same 10 to 20 mcg/mL. With low albumin, kidney or liver disease, or pregnancy, the unbound (free) level is a better guide; see Phenytoin (Free). One hospital list uses 7 to 20 mcg/mL for children.","sources":[{"title":"Dilantin (extended phenytoin sodium) capsules: prescribing information","url":"https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=86dd27d1-9cee-48ae-b55d-e2d2f7dbc593","publisher":"Viatris Specialty (DailyMed)","year":2023},{"title":"Phenytoin, Free and Total (test 0090141)","url":"https://ltd.aruplab.com/Tests/Pub/0090141","publisher":"ARUP Laboratories"},{"title":"Identification and characterization of critical values in therapeutic drug monitoring: a retrospective analysis","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC11106295/","publisher":"Scientific Reports","year":2024}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"Measures the total amount of phenytoin (Dilantin), a seizure medicine, in your blood. Your prescriber uses it to check your dose.","url":"https://bloodtesttracker.com/markers/phenytoin","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}