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Endocrine & Reproductive
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Currently under review
Pending specialist review and validation.
This test measures thyroid stimulating hormone in your blood. TSH is made by the pituitary gland and signals your thyroid to produce the hormones thyroxine and triiodothyronine. Because the pituitary adjusts TSH in response to circulating thyroid hormones, this test reflects how the brain and thyroid communicate.
It is a standard blood draw, often ordered together with tests that directly measure thyroid hormones. Your clinician may use it to check thyroid function in people with symptoms, to monitor therapy, and to assess thyroid status across different ages, including infants and children when appropriate.
TSH is the primary screening and monitoring test for thyroid function. It helps detect an underactive or overactive thyroid, guides treatment decisions, and helps tailor doses of thyroid hormone replacement or antithyroid medications. It is also useful when symptoms are nonspecific, such as fatigue, changes in weight, mood shifts, or heart rhythm concerns.
During pregnancy, appropriate thyroid function supports maternal health and fetal development, so clinicians often use TSH, along with other thyroid tests, for careful monitoring. TSH can also help uncover pituitary problems that affect thyroid regulation, although additional testing is needed in that situation.
Higher than expected TSH usually suggests the thyroid is not making enough hormone, while lower than expected TSH can point to an overactive thyroid. Results need to be interpreted with your symptoms, physical exam, and other labs such as free thyroxine. In some conditions that involve the pituitary or in severe illness, the usual patterns may not apply, so your clinician may add tests or repeat the sample.
If you take thyroid medication, TSH can take time to reflect dose changes. Your clinician may ask about supplements, including biotin, and the timing of your dose before the blood draw. If a result does not fit how you feel, a repeat test or additional thyroid hormone measurements may be recommended.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
High dose biotin, often found in hair and nail products, can interfere with some immunoassays and may falsely lower TSH results. Stop nonessential biotin before testing per your clinician’s advice.
Taking levothyroxine shortly before the blood draw, or missing recent doses, can shift results. Aim for consistent timing from day to day, and ask whether to take your dose before or after the test.
Drugs such as amiodarone, lithium, high dose glucocorticoids, dopamine, and somatostatin analogs can alter TSH regulation or assay results. Provide a full medication and supplement list.
Recent severe illness, surgery, or major physiological stress can temporarily change thyroid test patterns. Your clinician may defer or repeat testing once you recover.
TSH has a daily rhythm, with levels varying over the day. When possible, use similar timing for repeat tests to improve comparison over time.
Pregnancy alters thyroid physiology and TSH targets differ from the nonpregnant state. Testing may be more frequent, and interpretation uses pregnancy-specific context.
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