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Total Thyroxine (Total T4)

Published: July 27, 2026Updated: August 25, 2026

Total T4 measures the total amount of thyroxine, a hormone produced by the thyroid gland, in the bloodstream. It is used to evaluate thyroid function and diagnose thyroid disorders.

Quick summary

Total T4 measures the total amount of thyroxine hormone in the blood to assess thyroid function.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
μg/dL
Clinical utility
diagnostic
Result kind
quantitative
FDA-cleared
Roche T4, Abbott T4, Siemens T4
interpretation: {"text":"May indicate hypothyroidism, iodine deficiency, or a non-thyroidal illness.","label":"Low Total T4"}; {"text":"May suggest hyperthyroidism, thyroiditis, or excessive thyroid hormone intake.","label":"High Total T4"}

Total T4, or total thyroxine, is a crucial biomarker that quantifies the total concentration of thyroxine hormone in the blood. Thyroxine is one of the primary hormones produced by the thyroid gland and plays a vital role in regulating metabolism, growth, and development.

The test for Total T4 is often used in conjunction with other thyroid function tests, such as TSH (thyroid-stimulating hormone) and Free T4, to provide a comprehensive assessment of thyroid health. Abnormal levels of Total T4 can indicate hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid).

Reference ranges for Total T4 are typically between 4.5 and 12 μg/dL. Values outside this range may necessitate further investigation or treatment. Factors such as pregnancy, certain medications, and concurrent illnesses can influence Total T4 levels.

Frequently asked questions

What is the normal range for Total T4?
The normal range for Total T4 is typically between 4.5 and 12 μg/dL.
Can Total T4 levels be affected by medications?
Yes, certain medications such as steroids, anticonvulsants, and lithium can affect Total T4 levels.
  1. 1
    American Thyroid AssociationSource
  2. 2
    Mayo ClinicSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy