![]() Investigation of abnormal TSH in non-pregnant adults. This physiology is important in the diagnosis and therapy of thyroid disorders (Figure 1).įigure 1. T4 is converted to the biologically active T3 by deiodinase enzymes. TSH is the driver hormone for intrathyroidal synthesis of the pro-hormone T4, which constitutes approximately 90% of the hormonal secretion from the thyroid, along with a small amount of T3. Once an abnormal TSH level is detected, it must be interpreted with reference to thyroid hormone levels. In contrast, hyperthyroidism is commonly symptomatic, with higher clinical and biochemical correlation. 5,6 If pre-test probability is high, a concordant measure of a normal FT4 with a normal TSH result confidently excludes incident thyroid dysfunction. With few exceptions, a TSH result within the normal range (generally 0.5–4.0 mIU/L, and reported for each assay) in a setting of low pre-test probability excludes thyroid dysfunction and generally does not require repeating for several years. Therefore, TSH is often used as a screening test in a wide range of clinical presentations with low pre-test probability for thyroid disease, including fatigue, metabolic syndrome and mental health disorders. Symptoms of hypothyroidism are non-specific and have poor correlation with thyroid hormone deficiency. For these reasons, and because central thyroid dysfunction (pituitary or hypothalamic disorders) is rare, a normal TSH level largely excludes thyroid hormone excess or deficiency. 3 Assays for TSH are robust, and interference is uncommon. A small rise in thyroid hormone production leads to a logarithmic suppression of TSH, and vice versa, meaning that TSH is a very sensitive marker of thyroid dysfunction. TSH release from the anterior pituitary is tightly controlled by a negative feedback loop from the circulating thyroid hormones thyroxine (T4) and triiodothyronine (T3). Measurement of TSH is a screening test for suspected thyroid dysfunction. prior to, and early in the first trimester of, pregnancy in women treated with levothyroxine or those with risk factors for thyroid dysfunction.when monitoring uncomplicated thyroxine replacement therapy, with a minimum interval of 4–6 weeks following a dose change to allow achievement of a steady state, and annually when stable.when goitre or thyroid nodules are identified.when screening for thyroid hormone excess or deficiency on the basis of symptoms or risk factors.Thyroid stimulating hormone (TSH) should be checked: When should thyroid stimulating hormone be checked? This article provides succinct recommendations for the investigation of suspected thyroid disorders in adults. 2 It is important that suspected thyroid abnormalities are investigated appropriately to minimise patient anxiety, inefficiency and cost. 1 Of the five NPS MedicineWise ‘Choosing Wisely’ initiatives in endocrinology, two relate to thyroid investigation. Lab Tests Online UK has more information about the different types of thyroid function tests and thyroid antibody tests.Australian data show that thyroid tests are ordered at least once per every 100 problems managed in general practice. A thyroid antibody test is only likely to be recommended if the GP suspects you have an autoimmune thyroid condition. This is to help diagnose or rule out autoimmune thyroid conditions, such as Hashimoto's thyroiditis. ![]() Less commonly, a thyroid antibody test may be recommended after a thyroid function test. The GP may recommend that you have a repeat blood test every so often to see whether you eventually develop an underactive thyroid.īlood tests are also sometimes used for other measurements, such as checking the level of a hormone called triiodothyronine (T3). If your test results show raised TSH but normal T4, you may be at risk of developing an underactive thyroid in the future. The test, called a thyroid function test, looks at levels of thyroid-stimulating hormone (TSH) and thyroxine (T4) in the blood.ĭoctors may refer to this as "free" T4 (FT4).Ī high level of TSH and a low level of T4 in the blood could mean you have an underactive thyroid. Thyroid function testĪ blood test measuring your hormone levels is the only accurate way to find out whether there's a problem. Therefore, you should see a GP and ask for a blood test if you repeatedly have symptoms of an underactive thyroid. This can cause high cholesterol and atherosclerosis (clogging of the arteries), which can potentially lead to serious heart-related problems, such as angina and a heart attack. Low levels of thyroid-producing hormones, such as triiodothyronine (T3) and thyroxine (T4), can change the way the body processes fat. It's very important that an underactive thyroid (hypothyroidism) is diagnosed as soon as possible.
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