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An increase in TSH above the normal range indicates under-replacement or poor compliance with therapy. A significant reduction in TSH suggests over-treatment. In both cases, a change in dose may be required. A low or low-normal TSH value may also signal pituitary disease in the absence of replacement. [citation needed]
Goiter is the general enlargement of the thyroid that can be associated with many thyroid diseases. The main reason this happens is because of increased signaling to the thyroid by way of TSH receptors to try to make it produce more thyroid hormone. [9] This causes increased vascularity and increase in size (hypertrophy) of the gland. [9]
Graves' disease is the cause of about 50% to 80% of the cases of hyperthyroidism in the United States. [1] [7] Other causes include multinodular goiter, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. [1] [2] A less common cause is a pituitary adenoma. [1]
Other types may not stimulate the thyroid gland, but prevent TSI and TSH from binding to and stimulating the receptor. Another effect of hyperthyroidism is bone loss from osteoporosis, caused by an increased excretion of calcium and phosphorus in the urine and stool. The effects can be minimized if the hyperthyroidism is treated early.
The increased hip fracture rates later in life in turn cause excess late mortality. [citation needed] The changes in bone metabolism are connected with negative calcium balance, an increased excretion of calcium and phosphorus in the urine (hypercalciuria) and stool, and, rarely, hypercalcemia. [13]
The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland.
Thyroid function tests (TFTs) is a collective term for blood tests used to check the function of the thyroid. [1] TFTs may be requested if a patient is thought to suffer from hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid), or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy.
The elevation is usually a marked increase over the normal range. [13] TSH is the preferred initial test of thyroid function as it has a higher sensitivity to changes in thyroid status than free T 4. [64] Biotin can cause this test to read "falsely low". [21]
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