Thyroxine (T4) is the major hormone produced by the thyroid gland.

It is converted into T3 (triiodothyronine), the more active form, in peripheral tissues.

Clinical uses include:

Diagnosing hyperthyroidism (overactive thyroid).

Supporting evaluation of hypothyroidism (underactive thyroid).

Monitoring thyroid replacement therapy.

Assessing thyroid gland function in conjunction with T3 and TSH tests.

Often performed alongside TSH and Free T4 tests for a complete thyroid profile.

Analyte: Total Thyroxine (T4) in serum (µg/dL).

Normal Range (varies by lab): ~5–12 µg/dL.

Abnormal Findings:

High T4: Hyperthyroidism, Graves’ disease, thyroid nodules, excessive thyroid hormone therapy.

Low T4: Hypothyroidism, pituitary or hypothalamic dysfunction, chronic illness.

Clinical Use:

Provides a direct measure of thyroid hormone production.

Helps guide diagnosis and management of thyroid disorders.

Supports endocrinology and internal medicine evaluations.