Hi and welcome to the forum! I am glad that I can help you.
In normal individuals there is a positive control connection between the pituitary gland and the thyroid gland. This means that if the FT4 and FT3 hormone levels are low, then the pituitary gland produces TSH as a result of the impulses of the thalamus(the releasing factors). TSH is the hormone that stimulates the thyroid gland to produce FT4 and FT3 hormones. In other words: 1. if the levels of FT4 and FT3 are low, the level of TSH should be higher; and 2. if the levels of FT4 and FT3 are high, the level of TSH should be lower. In certain conditions such as those affecting the pituitary or thyroid glands, the levels of any of these hormone can be increased.
Given the data that you described, of decreased TSH, normal FT4, but increased FT3, you may be experiencing a node on the thyroid gland. This node may be hormone productive. You may consider having a nuclear scan of the thyroid gland. If diagnosed with a node, you might need to have a biopsy to rule out a malignant tumor. You might also consider seeing an endocrinologist for further advice and diagnosis of your current condition.
Please keep in mind that I provide medical information only. I am not able to diagnose medical conditions online. Please contact your doctor or other qualified healthcare provider such as an endocrinologist for further advice and information about diagnosis and treatment options.
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