Thyroxine (T4)

Thyroxine is also called T4. T4 is a hormone that your thyroid gland makes. A T4 test measures the level of T4 in a sample of your blood. Too much or too little T4 may be a sign of a thyroid problem.

A T4 test is usually used with other thyroid tests to help diagnose and monitor thyroid disease and to gather more information about other conditions that may affect your thyroid.

Source: MedlinePlus, U.S. National Library of Medicine

Normal range

15 published ranges, each from a named source

4.511.7 ug/dL drawn: 20 y+ · ARUP Laboratories Test Directory

20 y+: 4.5–11.7 ug/dL

Ranges from ARUP Laboratories Test Directory, Mayo Clinic Laboratories (Pediatric Test Catalog).

All source ranges (15)

Source	Sex	Age	Range
ARUP Laboratories Test Directory	All	≤ null d	6.6–17.5 ug/dL
ARUP Laboratories Test Directory	All	≤ 3 d	5.37–22.4 ug/dL
ARUP Laboratories Test Directory	All	4 d – 30 d	5.24–23.2 ug/dL
ARUP Laboratories Test Directory	All	30 d – 2 y	5.37–16 ug/dL
ARUP Laboratories Test Directory	All	2 y – 6 y	5.26–14.8 ug/dL
ARUP Laboratories Test Directory	All	7 y – 11 y	5.7–14.1 ug/dL
ARUP Laboratories Test Directory	All	12 y – 19 y	4.74–14.6 ug/dL
ARUP Laboratories Test Directory	All	20 y+	4.5–11.7 ug/dL
Mayo Clinic Laboratories (Pediatric Test Catalog)	All	≤ 5 d	5–18.5 ug/dL
Mayo Clinic Laboratories (Pediatric Test Catalog)	All	6 d – 2 mo	5.4–17 ug/dL
Mayo Clinic Laboratories (Pediatric Test Catalog)	All	3 mo – 11 mo	5.7–16 ug/dL
Mayo Clinic Laboratories (Pediatric Test Catalog)	All	1 y – 5 y	6–14.7 ug/dL
Mayo Clinic Laboratories (Pediatric Test Catalog)	All	6 y – 10 y	6–13.8 ug/dL
Mayo Clinic Laboratories (Pediatric Test Catalog)	All	11 y – 19 y	5.9–13.2 ug/dL
Mayo Clinic Laboratories (Pediatric Test Catalog)	All	20 y+	4.5–11.7 ug/dL

What an abnormal result can be associated with

A high result: Increased circulating T4 concentration
A low result: Decreased circulating T4 concentration

Associations from LOINC2HPO (Human Phenotype Ontology). This is reference information, not a diagnosis: only a clinician can interpret your result in context.

details

Sample: Serum or plasma · LOINC
Listed under: Hyperthyroidism · Hypothyroidism · Thyroid Diseases
Code: LOINC 3026-2 · ug/dL
Also known as: L-thyroxine, Levo-thyroxine, Levothyroxine, TT4, Thyrox

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