FT4

Thyroid hormones regulate metabolism, energy generation, and overall hormonal balance. FT4, or Free T4 (游離甲狀腺素), is a key indicator of thyroid health, providing valuable insights into the functioning of this vital gland. Understanding FT4 levels is essential for diagnosing and managing thyroid disorders. 

What is FT4? 

The thyroid gland, an endocrine (“ductless”) organ hugging the wind-pipe in the neck, produces one of the major metabolically active hormones in the human body, tetraiodothyronine or thyroxine, T4.  T4 is usually released in the bloodstream in protein-bound and free form. The protein-bound T4 is rendered metabolically inactive while the unbound or free T4 is biologically active that is readily available for the body’s tissues to use. Free T4 (FT4) is thus of significant clinical utility when it comes to overall health and metabolism. 

What is FT4 Thyroid Test? 

The FT4 thyroid test measures the level of free or “unbound" T4 in the bloodstream. It is part of the standard diagnostic tool to evaluate thyroid function and diagnose thyroid diseases. The test is typically ordered if a patient shows symptoms of thyroid dysfunction, which can include fatigue, weight changes, temperature sensitivity, and changes in heart rate. It may also be part of a comprehensive thyroid panel that includes Thyroid Stimulating Hormone (TSH) and T3 (Triiodothyronine) tests. 

What is the Normal Laboratory Range for FT4? 

The normal range for FT4 varies slightly between laboratories but generally between 0.7 to 1.9 ng/dL (nanograms per deciliter). It's important to note that these values can differ based on the measurement methods used by different labs. Factors such as age, sex, and pregnancy can also influence what is considered an average FT4 level. Always discuss your results with your healthcare provider to understand their meaning in your context. 

What Causes High FT4? What are the symptoms? 

Findings of high FT4 levels in the body usually correspond to a hyperfunctioning or hyperactive thyroid, a condition known as hyperthyroidism. This is commonly found in Graves disease, toxic multinodular goiter (TMNG) and toxic adenoma (TA). Excess FT4 can cause symptoms such as palpitations, high body temperature, heat intolerance, tremors, excessive sweating, nervousness/anxiety, weight loss and diarrhea. 

And What Causes Low FT4? What are the symptoms? 

On the other hand, findings of low FT4 levels in the body correspond to a hypofunctioning or hypoactive thyroid, a condition known as hypothyroidism. This is commonly found in iodine deficiency, autoimmune thyroid disease such as Hashimoto’s thyroiditis and after thyroid surgery or radiation therapy. FT4 deficiency can manifest as cold intolerance, hair loss, fatigue, weight gain, sleep disturbances and constipation. 

How to Lower FT4? 

Lowering high FT4 levels typically involves addressing the underlying cause which is an overactive thyroid. Treatment strategies may include: 

• Medication: Anti-thyroid medications such as Methimazole or Propylthiouracil can be used to reduce thyroid hormone production. Beta blockers such as propranolol and atenolol can reduce the rapid heart rate/palpitations and tremors. 

• Radioactive Iodine Therapy: This treatment involves taking radioactive iodine orally. The iodineradiation then accumulates in the thyroid gland and destroys overactive thyroid cells. 

• Surgery: In some cases, a part or all of the thyroid gland may be surgically removed. 

• Dietary Changes: While no diet can cure hyperthyroidism, certain foods, such as those high in calcium and selenium, may help reduce symptoms or complement other treatments. 

How is low FT4 increased? 

Meanwhile, a low FT4 as a consequence of hypothyroidism, can be managed as follows: 

• Hormone replacement: Levothyroxine is the primary drug of choice in treating hypothyroidism, especially in post-surgical or radiation therapy patients as means of replacing the active thyroid hormone. 

• Iodine supplementation: In iodine-deficient endemic areas, iodine supplementation or iodine-fortified food or salt is encouraged to combat goiter, the clinical enlargement of the thyroid gland due to lack of iodine and the resultant hypothyroidism. 

FT4 is a critical marker of thyroid health, influencing various physical functions and overall well-being. Whether you are experiencing symptoms of a thyroid disorder or just monitoring your health, understanding the role of FT4 and maintaining it within the normal range is essential. Regular testing and consultation with healthcare professionals will ensure that deviations are managed promptly and effectively, contributing to better health outcomes.