Typical reference ranges
| TSH (mIU/L) | Usually described as |
|---|---|
| Below 0.1 | Suppressed: overactive thyroid or high thyroxine dose likely |
| 0.1–0.4 | Low |
| 0.4–4.0 | Typical adult range |
| 4.0–10 | Raised: often subclinical hypothyroidism if T4 is normal |
| Above 10 | Clearly raised: underactive thyroid likely |
Ranges based on: MedlinePlus; American Thyroid Association; ATA 2017 guidelines for thyroid disease during pregnancy. Full references are listed at the end of this page.
Use your own lab's range. Reference ranges differ between labs, analysers and methods, and with age, sex and pregnancy. The range printed on your report takes priority over the figures here.
Check your value
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General information only, not a diagnosis. Your lab's printed range takes priority.
Why TSH goes up and down
The pituitary gland watches the level of thyroid hormone in the blood. When it is low, the pituitary releases more TSH to push the thyroid harder; when it is high, TSH falls. That feedback is why TSH is a sensitive early marker.
Causes of high TSH
- Hashimoto's thyroiditis, the most common cause of hypothyroidism
- Iodine deficiency, still seen in parts of South Asia and Africa
- Previous thyroid surgery or radio-iodine treatment
- Too low a thyroxine dose, or thyroxine taken with food, calcium or iron
- Recovery from a recent illness (TSH can rise temporarily)
Causes of low TSH
- Graves' disease, toxic thyroid nodules or thyroiditis
- Too high a thyroxine dose
- Early pregnancy (normal physiological fall)
- Steroids and serious illness
- Rarely, a pituitary problem (then free T4 is low too)
Age matters
TSH tends to drift upward with age, so a mildly raised TSH in someone in their 70s or 80s can be normal for their age. Many doctors avoid treating a mildly raised TSH in older adults without symptoms.
Frequently asked questions
What is a normal TSH for a woman?
The same as for men: about 0.4–4.0 mIU/L outside pregnancy.
What TSH is normal in pregnancy?
Lower than usual, especially in the first trimester. Ask for trimester-specific ranges; around 4.0 mIU/L is a common upper limit.
Can stress change TSH?
Severe illness and some medicines can change it. Everyday stress has little effect.
Is mIU/L the same as µIU/mL?
Yes, the numbers are identical.
Sources and references
- MedlinePlus: TSH Test
- American Thyroid Association: Thyroid Function Tests
- ATA 2017 guidelines for thyroid disease during pregnancy