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Understand Thyroid-Stimulating Hormone (TSH)

Thyroid-Stimulating Hormone (TSH)

Hormone markers

What the test generally measures, and what to ask about it.

Longetic keeps every lab and record you’ve had organized and easy to find, so your own Thyroid-Stimulating Hormone (TSH) values sit together on one chart and you walk into your next appointment prepared.

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Updated Jul 3, 2026

What is Thyroid-Stimulating Hormone (TSH)?

A pituitary hormone that signals the thyroid gland to produce thyroid hormone.

Thyroid-stimulating hormone (TSH) is released by the pituitary gland to regulate how much hormone the thyroid produces. TSH is usually the first test doctors order to check thyroid function: high TSH can indicate an underactive thyroid (hypothyroidism), while low TSH can indicate an overactive thyroid (hyperthyroidism).

Tests often checked alongside this

  • Free T4 — shows whether the thyroid itself is under- or overactive
  • Free T3 — added when symptoms persist despite normal TSH/T4
  • TPO antibodies — checks for autoimmune thyroid conditions like Hashimoto's

How this can show up in how you look and feel

  • High TSH (underactive thyroid) can be associated with fatigue, weight gain, or dry skin
  • Hair thinning, including eyebrows, is sometimes associated with thyroid imbalance
  • Low TSH (overactive thyroid) can be associated with weight loss, anxiety, or heat intolerance
  • Cold intolerance and brittle nails are sometimes noticed with thyroid changes

What can affect this marker

  • Time of day it's drawn
  • Biotin supplements before testing
  • Medications like thyroid hormone
  • Pregnancy and life stage

What to track over time

  • Your trend across repeat tests
  • Energy, weight and mood alongside it
  • Response to any treatment changes
  • Alongside free T4 or T3 results

What to ask your doctor

  • Is my thyroid over- or underactive?
  • Should I pause biotin before retesting?
  • Do I need additional thyroid tests?
  • How often should this be checked?

This glossary entry is for informational purposes only and is not a substitute for professional medical advice. Read our Terms of Use.

References

"Thyroid-Stimulating Hormone, Sensitive (s-TSH), Serum - Test Catalog" Mayo Clinic Laboratories. www.mayocliniclabs.com/test-catalog/overview/8939. Accessed Jul 3, 2026.
"Thyroid Function Tests" American Thyroid Association. www.thyroid.org/thyroid-function-tests. Accessed Jul 3, 2026.
"TSH (Thyroid-Stimulating Hormone) Test" MSD Manual, Consumer Version. www.msdmanuals.com/home/multimedia/lab-tests/tsh-thyroid-stimulating-hormone-test. Accessed Jul 7, 2026.

About our sources

Clinical / professional

Medical societies, specialty colleges, and professional associations whose consensus statements reflect clinical practice standards.

Peer-reviewed research

Original research articles and systematic reviews published in indexed journals and verified through PubMed or DOI.

History of updates

Published · Jul 3, 2026
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