TT4 is the main product of thyroid secretion and is an essential ingredient in the integrity of the hypothalamic-pituitary gland. The TT4 measures can be used for the diagnosis of hyperthyroidism, primary and secondary, and TT4 inhibition of treatment.

Clinical Significance

✔ Abnormally high test results
Elevated T4 levels may indicate hyperthyroidism. They may also indicate other thyroid problems, such as thyroiditis or toxic multinodular goiter
Other reasons for abnormal results may include:
high levels of protein in the blood

• too much iodine
• too much thyroid replacement medication
• trophoblastic disease, a group of rare pregnancy related tumors
• germ cell tumors

Too much iodine can raise your T4 levels. Because X-ray dyes can include iodine, a recent X-ray involving dye may also raise your T4 test results

✔ Abnormally low test results
Abnormally low levels of T4 may indicate:

• dietary issues, such as fasting, malnutrition, or an iodine deficiency
• medications that affect protein levels
• Hypothyroidism
• Illness
• a pituitary problem

Intent Use

A T4 test is used to evaluate thyroid function and diagnose thyroid disease.