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Free 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

46 published ranges, each from a named source
19 y+
0.82–1.77 ng/dL
20 y+
0.9–1.7 ng/dL
Normal
0.8–2 ng/dL
Female · 18 y+
1.1–2.4 ng/dL
Male · 18 y+
1.1–2.4 ng/dL
Ranges from ARUP Laboratories Test Directory, LabCorp Test Directory, Laboratorium Medyczne Synevo (test catalog, synevo.pl), Mayo Clinic Laboratories (Pediatric Test Catalog), Mayo Clinic Laboratories (Test Catalog).

All source ranges (46)
SourceSexAgeRange
ARUP Laboratories Test Directory All ≤ 3 d 0.7–2.7 ng/dL
ARUP Laboratories Test Directory All 4 d – 30 d 0.8–3.1 ng/dL
ARUP Laboratories Test Directory All 30 d – 2 y 0.5–2.3 ng/dL
ARUP Laboratories Test Directory All 2 y – 6 y 0.9–1.8 ng/dL
ARUP Laboratories Test Directory All 7 y – 11 y 0.9–1.7 ng/dL
ARUP Laboratories Test Directory All 12 y – 19 y 0.9–1.6 ng/dL
ARUP Laboratories Test Directory All 20 y+ 0.9–1.7 ng/dL
ARUP Laboratories Test Directory Female ≤ 7 d 2.2–5.3 ng/dL
ARUP Laboratories Test Directory Female 14 d – 21 d 0.9–4 ng/dL
ARUP Laboratories Test Directory Female 30 d – 5 mo 1.1–2.2 ng/dL
ARUP Laboratories Test Directory Female 6 mo – 6 y 1.4–2.7 ng/dL
ARUP Laboratories Test Directory Female 7 y – 17 y 1.1–2 ng/dL
ARUP Laboratories Test Directory Female 18 y+ 1.1–2.4 ng/dL
ARUP Laboratories Test Directory Male ≤ 7 d 2.2–5.3 ng/dL
ARUP Laboratories Test Directory Male 14 d – 21 d 0.9–4 ng/dL
ARUP Laboratories Test Directory Male 30 d – 5 mo 1.1–2.2 ng/dL
ARUP Laboratories Test Directory Male 6 mo – 6 y 1.4–2.7 ng/dL
ARUP Laboratories Test Directory Male 7 y – 17 y 1.1–2 ng/dL
ARUP Laboratories Test Directory Male 18 y+ 1.1–2.4 ng/dL
LabCorp Test Directory All ≤ 3 d 0.66–2.71 ng/dL
LabCorp Test Directory All 4 d – 30 d 0.83–3.09 ng/dL
LabCorp Test Directory All 1 mo – 1 y 0.48–2.34 ng/dL
LabCorp Test Directory All 1 y – 5 y 0.85–1.75 ng/dL
LabCorp Test Directory All 6 y – 10 y 0.9–1.67 ng/dL
LabCorp Test Directory All 11 y – 19 y 0.93–1.6 ng/dL
LabCorp Test Directory All 19 y+ 0.82–1.77 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All all ages 0.8–2 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All ≤ 5 d 0.9–2.5 ng/dL
Mayo Clinic Laboratories (Test Catalog) All ≤ 5 d 0.9–2.5 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All 6 d – 2 mo 0.9–2.2 ng/dL
Mayo Clinic Laboratories (Test Catalog) All 6 d – 2 mo 0.9–2.2 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All 3 mo – 11 mo 0.9–2 ng/dL
Mayo Clinic Laboratories (Test Catalog) All 3 mo – 11 mo 0.9–2 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All 1 y – 5 y 1–1.8 ng/dL
Mayo Clinic Laboratories (Test Catalog) All 1 y – 5 y 1–1.8 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All 6 y – 10 y 1–1.7 ng/dL
Mayo Clinic Laboratories (Test Catalog) All 6 y – 10 y 1–1.7 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All 11 y – 19 y 1–1.6 ng/dL
Mayo Clinic Laboratories (Test Catalog) All 11 y – 19 y 1–1.6 ng/dL
Mayo Clinic Laboratories (Pediatric Test Catalog) All 20 y+ 0.9–1.7 ng/dL
Mayo Clinic Laboratories (Test Catalog) All 20 y+ 0.9–1.7 ng/dL
Laboratorium Medyczne Synevo (test catalog, synevo.pl) All ≤ 3 d 22–49 pmol/L
Laboratorium Medyczne Synevo (test catalog, synevo.pl) All 3 d – 2 mo 9–21 pmol/L
Laboratorium Medyczne Synevo (test catalog, synevo.pl) All 2 mo – 1 y 8–17 pmol/L
Laboratorium Medyczne Synevo (test catalog, synevo.pl) All 1 y – 5 y 9–20 pmol/L
Laboratorium Medyczne Synevo (test catalog, synevo.pl) All 5 y – 14 y 8–17 pmol/L

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
Part of
Bryan Johnson Blueprint
Monitored for
Hypothyroidism
Listed under
Hyperthyroidism · Thyroid Diseases
Code
LOINC 3024-7 · ng/dL
Also known as
Thyroxine (T4) free, FT4, L-thyroxine, Levo-thyroxine, Levothyroxine
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