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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.
Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T 4), and then triiodothyronine (T 3) which stimulates the metabolism of almost every tissue in the body. [1]
Certain medications can have the unintended side effect of affecting thyroid function. While some medications can lead to significant hypothyroidism or hyperthyroidism and those at risk will need to be carefully monitored, some medications may affect thyroid hormone lab tests without causing any symptoms or clinical changes, and may not require treatment.
Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, Hashimoto's disease, and autoimmune thyroiditis is an autoimmune disease in which the thyroid gland is gradually destroyed. [7] [1] Early on, symptoms may not be noticed. [3] Over time, the thyroid may enlarge, forming a painless goiter. [3]
The syndrome can present with variable symptoms, even between members of the same family harboring the same mutation. [1] Typically most or all tissues are resistant to thyroid hormone, so despite raised measures of serum thyroid hormone the individual may appear euthyroid (have no symptoms of over- or underactivity of the thyroid gland).
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.
Therefore, when TRH is given exogenously, TSH levels increase. If the increase in serum TSH level following TRH administration is absent or very slight, then the cause of the hypothyroidism is in the anterior pituitary gland, i.e. the pituitary is not secreting TSH. Therefore, even when TRH is given exogenously, TSH levels do not rise as the ...
Subclinical hypothyroidism, a milder form of hypothyroidism characterized by normal thyroxine levels and an elevated TSH level, is thought to occur in 4.3–8.5% of people in the United States. [8] Subclinical hypothyroidism has been associated with an increased risk of atrial fibrillation (AF) and is the most frequent thyroid abnormality in ...