Thyroid TSH Reference Guide
TSH (thyroid stimulating hormone) is the main screening test for thyroid problems. Learn what high and low TSH mean.
The Thyroid TSH Reference Guide is being built
This free reference guide will appear here shortly. Meanwhile, the formula and ranges below show exactly how it works.
- TSH (mIU/L)
- Pregnant (yes / trimester)
- Age
- Low / normal / high
- What it may mean
About the Thyroid TSH Reference Guide
TSH is made by the pituitary gland in the brain. When the thyroid is underactive, TSH rises; when it is overactive, TSH falls.
Reference ranges & how it works
Typical adult reference range:
TSH ≈ 0.4–4.0 mIU/L (varies by lab, often up to 4.5–5.5)
High TSH → suggests hypothyroidism (underactive thyroid). Low TSH → suggests hyperthyroidism (overactive thyroid). Doctors read TSH together with free T4 and T3.
Pregnancy uses lower, trimester-specific ranges — follow your doctor’s targets.
Frequently asked questions
Do I need to fast for a thyroid test?
Fasting is usually not needed. Test at a similar time each day, and if you take thyroid tablets, follow your doctor’s advice on whether to take them before the test.
What are the symptoms of thyroid problems?
Underactive: tiredness, weight gain, feeling cold, constipation, dry skin. Overactive: weight loss, fast heartbeat, anxiety, heat intolerance.
Medical disclaimer: These tools give general information and estimates only. They are not a diagnosis and do not replace advice from a qualified doctor. Always talk to your doctor about your results, and seek urgent medical help in an emergency.