Understanding Your TSH
TSH (Thyroid Stimulating Hormone) is the most common test for checking how your thyroid is working. Your thyroid controls your metabolism, so it affects energy, weight, mood, and more.
What TSH Measures
TSH is a hormone made by your pituitary gland, a small gland in your brain. Its job is to tell your thyroid how much thyroid hormone to produce.
TSH works like a thermostat. When thyroid hormone is low, the brain raises TSH to push the thyroid to work harder. When thyroid hormone is high, TSH drops. That is why a high TSH usually means an underactive thyroid, and a low TSH usually means an overactive one.
What Your Results Can Mean
| Result | What It Means |
|---|---|
| High TSHUnderactive Thyroid (Hypothyroidism) | Your thyroid is not making enough hormone. This can cause fatigue, weight gain, feeling cold, dry skin, constipation, and low mood. |
| Low TSHOveractive Thyroid (Hyperthyroidism) | Your thyroid is making too much hormone. This can cause anxiety, a racing heart, weight loss, feeling hot, and trouble sleeping. |
| Normal TSHBalanced Thyroid Function | Your thyroid is most likely working normally. |
Follow-Up Tests
If your TSH is abnormal, we may add other tests, such as Free T4 and Free T3 (the actual thyroid hormones) or thyroid antibodies, to understand the cause and guide treatment.
What’s Most Important to Know
TSH is very sensitive, and a mildly abnormal value does not always mean you need treatment. We look at your TSH alongside your symptoms and, when needed, repeat or add tests before making decisions.
If you are already on thyroid medication, TSH is the main number we use to fine-tune your dose. Dr. Mui will review your result in the context of how you are feeling.
This page is for general education and does not replace a conversation with your doctor about your specific results. Want to review your results? Book a visit and we’ll go through them together.