Thyroid Function Panel (Free T3, Free T4, TSH)

Function

The Thyroid Function Panel is a comprehensive group of tests used to evaluate the health and efficiency of the thyroid gland. The thyroid, a butterfly-shaped gland in the neck, produces hormones that regulate the body's metabolism, energy production, and sensitivity to other hormones. The primary regulator is Thyroid Stimulating Hormone (TSH), produced by the pituitary gland. When the pituitary senses low thyroid hormone levels, it releases TSH to stimulate the thyroid. Free T4 (Thyroxine) and Free T3 (Triiodothyronine) are the active forms of the hormones circulating in the blood. Free T3 is the most metabolically active, while T4 serves as a precursor. Together, these markers provide a snapshot of the Hypothalamic-Pituitary-Thyroid (HPT) axis.

Why it is Ordered

Physicians order this panel when a patient exhibits symptoms of an overactive thyroid (hyperthyroidism) or an underactive thyroid (hypothyroidism). Symptoms of hyperthyroidism include rapid heart rate, unexplained weight loss, anxiety, and heat intolerance. Conversely, hypothyroidism symptoms include fatigue, weight gain, depression, and cold intolerance. It is also used to monitor the effectiveness of thyroid replacement therapy (like levothyroxine) or anti-thyroid medications and to screen for subclinical thyroid disease where TSH is abnormal but T3/T4 levels remain within the reference range.

Associated Conditions

• Hashimoto's Thyroiditis: An autoimmune disorder and the most common cause of hypothyroidism.
• Graves' Disease: An autoimmune condition leading to hyperthyroidism.
• Thyroiditis: Inflammation of the thyroid gland which may cause a temporary leak of hormones.
• Pituitary Adenomas: Tumors that can cause secondary thyroid dysfunction by over or under-producing TSH.
• Goiter and Nodules: Physical enlargements or growths that may alter hormone production.