Thyroid . Patient guide
Thyroid-Stimulating Hormone (TSH)
Also known as: Thyrotropin
TSH is a pituitary hormone that signals the thyroid gland to produce more thyroid hormone. It is the most sensitive first-line test for thyroid function: a high TSH usually points to an underactive thyroid and a low TSH to an overactive one.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in mIU/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Typical adult range | 0.27 to 4.20 | mIU/L (varies slightly between UK labs) |
| Suggesting hypothyroidism | over 4.20 | |
| Suggesting hyperthyroidism | under 0.27 | |
| Treatment target on levothyroxine (NICE) | 0.4 to 4.0 |
What it is
The hypothalamus releases TRH, which stimulates the pituitary to release TSH, which in turn stimulates the thyroid gland to release T4 and T3. The system is a feedback loop: low thyroid hormones drive TSH up, and high thyroid hormones suppress it.
Why a clinician would order it
TSH is the cornerstone of thyroid testing. It is included in any work-up for fatigue, weight change, hair shedding, cold or heat intolerance, anxiety, palpitations, low mood, irregular periods, fertility review, and in patients taking levothyroxine.
If your level is outside the range
Symptoms of low TSH
- Anxiety, palpitations
- Tremor
- Weight loss
- Heat intolerance, sweating
- Loose stools
- Sleep disruption
What low can indicate. Hyperthyroidism (Graves disease, toxic nodule, thyroiditis), over-replacement with levothyroxine, recent illness (transient suppression), or rarely pituitary disease.
Symptoms of high TSH
- Fatigue
- Weight gain
- Cold intolerance
- Hair shedding
- Dry skin
- Constipation
- Low mood
What high can indicate. Primary hypothyroidism (Hashimoto thyroiditis is the commonest UK cause), under-replacement with levothyroxine, recovery from illness, or assay interference.
Testing tips
No fasting required. Morning sample is preferable as TSH follows a mild diurnal rhythm. If you take levothyroxine, take it AFTER the blood draw rather than before, to avoid a transient suppression of the result.
Where you can get this tested
Thyroid-Stimulating Hormone is included in the following WMG Health panels. Same-day appointments at our Harley Street clinic, with results clinician-reviewed.
Want a specific combination of markers we do not have a panel for? Build a custom panel and our clinicians will design one for you.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.