TSH (thyroid stimulating hormone) is the brain’s instruction to the thyroid gland. It is the first thing a doctor looks at to judge how the thyroid is doing. Here is what it means, in plain language.
| Category | Reference range |
|---|---|
| Adults | 0.4–4.0 mIU/L |
| Pregnancy | depends on the trimester (check with your doctor) mIU/L |
The range depends on the lab and the assay; some labs set the upper limit at 4.0–4.2. Always compare your result with the reference range printed on your own report.
The pituitary gland (a small area of the brain) runs the thyroid using TSH, much the way a thermostat runs a radiator. When there is too little thyroid hormone, the brain raises TSH to push the gland harder. When there is too much, it lowers TSH to ease off.
That is why TSH works back to front: a high TSH usually points to an underactive thyroid, and a low TSH to an overactive one.
A high TSH usually points to hypothyroidism — the thyroid is not doing enough, so the brain “shouts louder”.
A low TSH more often points to hyperthyroidism — the thyroid is overactive, and the brain “eases off the gas”.
Possible symptoms: palpitations, tremor, sweating, weight loss without eating differently, anxiety, trouble sleeping. The cause (Graves’ disease, for example) is established by your doctor from further tests.
TSH is a sensitive but indirect marker: it is almost always assessed together with thyroid hormones (free T4, sometimes free T3) and antibodies. A single TSH outside the range is a reason to look further, not a diagnosis on the spot.
TSH is affected by the time of day (higher in the morning), stress, some medicines and pregnancy — which is why the result has to be read in context.
No need to decode the numbers yourself: take a photo of the report and the app explains “TSH” and the rest in plain words — what is normal and what deserves attention.
Get the appOpen in TelegramMost often a high TSH means the thyroid is underactive (hypothyroidism): the brain raises TSH trying to push the gland harder. The final call, though, is made by a doctor looking at all the tests together.
Strict fasting is not required, but blood is usually taken in the morning, since TSH levels shift over the course of the day. Check the rules at your own lab.
In most cases a normal TSH is a good sign, but if you have symptoms your doctor may also order free T4 and antibodies so that nothing is missed.
This material is for general information only. It is not a medical opinion and does not replace a consultation with a doctor. Reference ranges depend on the laboratory and the method — rely on the range printed on your own report. Your doctor makes the final interpretation. This page is a translation of the Russian original. The medical review applies to the original text.
Ponyatno