![]() The utility of universal testing of TSH in the first trimester of pregnancy has not been established and is best limited to patients with risk factors for thyroid dysfunction or those treated with levothyroxine. Weight loss or gain, commencement or cessation of hormonal contraception/hormonal replacement, pregnancy or intercurrent illness can all change requirements for thyroid hormone and should prompt a review of TSH levels. Once the patient is stable on levothyroxine, TSH should be measured annually. 7 Monitoring free T3 (FT3) is not helpful in this situation because it is cellular T3, not circulating T3, that is of biological relevance. TSH testing should not be repeated until 4–6 weeks after a dose change to ensure a steady state is reached. In patients treated with levothyroxine, TSH is used to monitor adequacy of replacement. §Specialist referral not required if transient thyroiditisįT3, free triiodothyronine FT4, free thyroxine TFT, thyroid function test TPO, thyroid peroxidase TRAb, thyroid stimulating hormone receptor antibody TSH, thyroid stimulating hormone TSHoma, thyrotropinoma TSI, thyroid stimulating immunoglobulin ‡May require treatment, especially in younger patients and those planning pregnancy †If suspicion of underlying pituitary or hypothalamic disease or specific factor affecting TSH interpretation, perform TSH, FT4 +/– FT3 *This pattern can be seen in non-thyroidal illness or rarely in central hypothyroidism Amiodarone can cause several patterns of thyroid dysfunction, and abnormal thyroid function tests within six months of amiodarone use require specialist evaluation. ![]() Note: Non-thyroidal illness can cause several patterns of thyroid hormone disturbance however, the abnormalities are usually mild and resolve over time. 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. Australian data show that thyroid tests are ordered at least once per every 100 problems managed in general practice.
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