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Endocrine & Reproductive
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Currently under review
Pending specialist review and validation.
This test measures the amount of thyroid-stimulating hormone (TSH) in your blood. TSH is made by your pituitary gland and tells your thyroid gland how much thyroid hormone to produce. Thyroid hormones help regulate energy use, temperature, heart function, digestion, and many other body processes.
A small blood sample is taken from a vein. Because TSH reflects how your brain and thyroid communicate, it is often the first test used to check overall thyroid function and to monitor thyroid treatment over time.
TSH helps your clinician evaluate symptoms such as fatigue, weight change, sensitivity to cold or heat, changes in heart rate, mood shifts, and changes in hair or skin. It is commonly ordered when thyroid disease is suspected, when you have risk factors, or to monitor and adjust thyroid medication.
TSH is also important during pregnancy planning and pregnancy, after thyroid surgery or radioactive iodine therapy, and when monitoring conditions affected by thyroid status. Out-of-range results can suggest an underactive or overactive thyroid, each of which carries different health risks if not addressed.
Your clinician will interpret your TSH in the context of the reference range for your age and situation. A higher TSH usually suggests that your thyroid is underactive, while a lower TSH can suggest that it is overactive or that thyroid medication may be too strong. Temporary shifts can occur with illness, stress, or recent changes in medication.
If a result is borderline or unexpected, your clinician may repeat the test, check free T4 and sometimes free T3, look for thyroid antibodies, or review your medicines and supplements. Pregnancy, pituitary disorders, severe illness, and high-dose biotin can change results or how they are interpreted. Discuss timing of your medication and blood draw so your care team can give you the most accurate guidance.
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.
TSH follows a daily rhythm and can be temporarily lowered during acute illness. Testing when you are well and at a consistent time helps with comparison.
Thyroid hormone timing relative to the blood draw, amiodarone, lithium, steroids, dopamine, and high-dose biotin can affect TSH or the assay. Always list doses and timing.
Normal thyroid regulation shifts during pregnancy and the postpartum period. Tell your clinician if you are pregnant, planning pregnancy, or recently postpartum.
If the pituitary is not working normally, TSH may not reflect thyroid status well. In that case, free thyroid hormone tests are crucial for interpretation.
Iodinated contrast, radioiodine therapy, thyroid surgery, or major dose changes can alter TSH for weeks. Share recent procedures and treatment changes.
Different labs and methods can yield slightly different results. Rare interferences, such as heterophile antibodies or macro-TSH, can falsely shift values.
References