What does the Free T4 (FT4) - FT4 blood test mean? Get a free analysis of your blood test now. Here's what you get with our free analysis:
The Free T4 (FT4) test measures the amount of unbound thyroxine (T4) hormone in the blood. T4 is one of the main hormones produced by the thyroid gland and plays a crucial role in regulating metabolism, growth, and development. The 'free' portion refers to the T4 that is not bound to proteins and is thus biologically active. This test is essential for assessing thyroid function and diagnosing conditions such as hypothyroidism or hyperthyroidism. It is often used in conjunction with other thyroid tests, such as TSH, to provide a comprehensive picture of thyroid health.
A low Free T4 reading (below 0.7 ng/dL) typically indicates hypothyroidism, a condition where the thyroid gland is underactive and not producing enough thyroid hormones. This can lead to symptoms such as fatigue, weight gain, dry skin, hair loss, constipation, and depression. In some cases, a low FT4 with a normal TSH may suggest secondary hypothyroidism, which is caused by pituitary gland dysfunction. Low FT4 levels may also occur in severe illnesses or with certain medications. Further testing and clinical evaluation are necessary to determine the underlying cause and appropriate treatment.
A high Free T4 reading (above 1.8 ng/dL) generally indicates hyperthyroidism, a condition where the thyroid gland is overactive and producing excess thyroid hormones. This can result in symptoms such as anxiety, rapid heartbeat, unexplained weight loss, heat intolerance, tremors, and difficulty sleeping. In some cases, high FT4 levels may be due to thyroiditis, Graves’ disease, or toxic nodular goiter. Certain medications or pregnancy can also affect FT4 levels. A thorough clinical assessment and additional tests are typically required to determine the cause and appropriate management of elevated FT4 levels.