TSH (Thyroid Stimulating Hormone) is made by the pituitary gland in the brain. It tells your thyroid how much hormone to make, so it is the most sensitive single test of thyroid function.
- Normal range (adults)
- 0.4–4 mIU/L (0.4–4 µIU/mL)
- Sample
- Blood
- Fasting
- Not usually needed
- Also called
- Thyroid Stimulating Hormone, T.S.H, Thyrotropin, Thyroid Stimulating Hormone TSH
TSH normal range
| Group | mIU/LConventional units: US, South Asia | µIU/mLSI units: UK, Europe, Australia, international |
|---|---|---|
| Adults | 0.4–4 | 0.4–4 |
Pregnancy uses lower, trimester-specific TSH targets.
Your report may use either unit system; labs in the Gulf often print both. Ranges also vary slightly between laboratories, so the range printed on your own report is the one to go by.
Why is the TSH test done?
It is the first test for thyroid problems, used for symptoms such as tiredness, weight change, hair loss, feeling cold or hot, palpitations, irregular periods and in pregnancy.
What does a high TSH level mean?
A high TSH usually means your thyroid is underactive (hypothyroidism): the brain is pushing harder because thyroid hormone levels are low. Symptoms include tiredness, weight gain, constipation, dry skin, feeling cold and low mood.
Common causes
- Hashimoto's thyroiditis (autoimmune; the most common cause)
- Iodine deficiency
- After thyroid surgery or radioactive iodine
- Some medicines, such as lithium or amiodarone
- Recovery phase after an illness
Diet and lifestyle tips
- Use iodised salt in normal amounts, and include dairy, eggs and seafood
- Eat selenium sources: fish, eggs, Brazil nuts (1 to 2 a day is enough)
- Cooked cabbage, broccoli and cauliflower are fine; very large amounts of raw ones may have a small effect
- If you take levothyroxine, take it on an empty stomach and keep calcium, iron and soy at least 4 hours away
What does a low TSH level mean?
A low TSH usually means your thyroid is overactive (hyperthyroidism). Symptoms include weight loss, fast heartbeat, anxiety, tremor, heat intolerance and loose stools.
Common causes
- Graves' disease
- Thyroid nodules
- Thyroiditis
- Taking too much thyroid medicine
- Early pregnancy (a mild drop is normal)
Diet and lifestyle tips
- Avoid iodine supplements, kelp and seaweed products
- Reduce caffeine, which worsens palpitations and anxiety
- Eat calcium and vitamin D sources to protect your bones
- Eat enough calories and protein if you are losing weight
When should you see a doctor?
See a doctor about any abnormal TSH, ideally with a Free T4 result. A very low TSH with palpitations or chest pain needs prompt review. Pregnancy uses lower TSH targets.
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This page is for general education and is not a diagnosis. Normal ranges differ between laboratories, so always compare your result with the reference range printed on your own report, and discuss abnormal results with your doctor.