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If you have higher-than-normal T4 or free T4 levels, it could indicate thyrotoxicosis. This can result from several situations and conditions, including hyperthyroidism (overactive thyroid), thyroid inflammation (thyroiditis) and taking excessive amounts of thyroid medication.
Blood tests that measure the hormones T-4 and T-3 and thyroid-stimulating hormone (TSH) can confirm a diagnosis of hyperthyroidism. A high level of T-4 and a low level of TSH is common in people with hyperthyroidism.
Tests measuring free T4 – either a free T4 (FT4) or free T4 index (FTI) – more accurately reflect how the thyroid gland is functioning when checked with a TSH. The finding of an elevated TSH and low FT4 or FTI indicates primary hypothyroidism due to disease in the thyroid gland.
This thyroid test analyzer will help you understand your TSH, T3, T4, and other thyroid function test results. Select a test and enter your lab value to learn more.
There have been studies suggesting that higher levels of free T 4 in the blood may be associated with an increased risk of developing a solid cancers (for example, lung, breast, prostate, gastrointestinal (GI) cancers). Other studies have not agreed with this finding.
If the results show that TSH is high and T-4 is low, then the diagnosis is hypothyroidism. In some cases, the thyroid hormone T-3 may be measured as well. If the second test shows high TSH but T-4 and T-3 are in the standard range, then the diagnosis is a condition called subclinical hypothyroidism.
High T4 levels. A few different conditions can cause high levels on a free T4 test, including: Too much iodine in your diet; Benign (not cancer) tumor (thyroid adenoma) or nodules on your...
A free T4 test measures only the free T4 in your blood. Because free T4 is what’s available to your body for use, a free T4 test is often preferred over a total T4 test. Why do doctors perform a...
Thyroxine, also known as T4, is a type of thyroid hormone. A T4 test measures the level of T4 in your blood. Too much or too little T4 can be a sign of thyroid disease. There are two forms of T4 in your blood: Free T4 is the active form of thyroxine hormone that enters your tissues where it's needed.
Conversely, when thyroid hormone levels are high, TSH production decreases, leading to low TSH levels, indicating hyperthyroidism . Free T4 (Thyroxine) About 90% of the hormone produced by the thyroid gland is T4. Total T4 measures all the hormone in the blood, both bound to proteins (such as thyroxine-binding globulin) and unbound. Only the ...