{"id":"total-t4","name":"Total T4 (Thyroxine)","shortName":"Total T4","aliases":["Total T4","Thyroxine, Total","T4, Total","Thyroxine (T4)","TT4","Total thyroxine","Tiroxina total","Total Tetraiodothyronine","Tetraiodothyronine","Thyroxine, Total, Serum","Thyroxine, Total T4","T4 Total","Serum T4"],"abbreviations":["TT4"],"loinc":[{"code":"3026-2","primary":true},{"code":"14921-1","primary":false},{"code":"35226-0","primary":false}],"specimen":"serum-or-plasma","units":[{"ucum":"ug/dL","display":"µg/dL"},{"ucum":"nmol/L","display":"nmol/L"},{"ucum":"ng/mL","display":"ng/mL"}],"referenceRanges":[{"population":"20+","low":4.5,"high":12,"unit":"ug/dL","unitDisplay":"µg/dL","note":"Labcorp prints 4.5 to 12.0 µg/dL (electrochemiluminescence immunoassay). ARUP prints a very close 4.50 to 11.70 µg/dL for ages 20 and older. Neither lab splits the adult interval by sex. Total T4 rises by about 50% in pregnancy, so these adult intervals are not meant for pregnancy. Use the range printed on your own report.","sources":[{"title":"Thyroxine (T4) (test 001149)","url":"https://www.labcorp.com/tests/001149/thyroxine-t4","publisher":"Labcorp"},{"title":"Thyroxine, Total T4 (test 3005978)","url":"https://ltd.aruplab.com/Tests/Pub/3005978","publisher":"ARUP Laboratories"}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"Measures all the thyroid hormone thyroxine in your blood, both the part attached to carrier proteins and the small free part.","url":"https://bloodtesttracker.com/markers/total-t4","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}