TSH (Thyroid-Stimulating Hormone)
The master signal that controls your thyroid — and often the first number to shift when metabolism, energy, or mood go sideways.
Track This Free → ← All BiomarkersWhat Is TSH?
TSH, or thyroid-stimulating hormone, is a hormone released by your pituitary gland that tells the thyroid how much thyroid hormone to make, and it is the primary screening test for thyroid function because it moves before free T4 and T3 do.
TSH works on a feedback loop: when thyroid hormone is low, the pituitary raises TSH to push the thyroid harder, so a high TSH usually signals an underactive thyroid (hypothyroidism). When thyroid hormone is high, TSH drops, so a low TSH usually signals an overactive thyroid (hyperthyroidism). This inverse relationship trips people up — a high TSH means a slow thyroid, not a fast one.
TSH Normal Range and Reference Values
| Category | Value | Notes |
|---|---|---|
| Normal (most labs) | 0.4–4.0 mIU/L | — |
| Subclinical hypothyroid | 4.0–10.0 mIU/L | (with normal T4) |
| Overt hypothyroid | Above 10 mIU/L | (with low T4) |
| Hyperthyroid | Below 0.4 mIU/L | (with high T4/T3) |
What Causes TSH to Change
The most common drivers behind a change in TSH are:
- Hashimoto's thyroiditis — the most common cause of a high TSH
- Iodine deficiency or, less often, excess
- Thyroid surgery or radiation history
- Graves' disease, which drives TSH low and thyroid hormone high
- Certain medications including lithium and amiodarone
- Pregnancy and the postpartum period, which shift thyroid demand
How Hunuu Tracks TSH
TSH is logged through the BODY pillar's Add Lab Result form. Because thyroid dysfunction shows up in the exact signals Hunuu already tracks — resting heart rate, HRV, energy, sleep, and mood — Hunuu presents your TSH next to those trends, so a borderline lab value is read alongside the day-to-day symptoms that make it clinically meaningful.
Frequently Asked Questions
What is a normal TSH level?
Most labs use a normal range of about 0.4 to 4.0 mIU/L. Some clinicians and guidelines use a tighter upper limit. Optimal ranges can also differ in pregnancy and by age.
Does high TSH mean an underactive or overactive thyroid?
High TSH usually means an underactive thyroid (hypothyroidism). The pituitary raises TSH to try to stimulate a thyroid that is not producing enough hormone. Low TSH usually points to an overactive thyroid.
What are symptoms of high TSH?
A high TSH from hypothyroidism can cause fatigue, weight gain, cold intolerance, dry skin, constipation, low mood, and slowed heart rate. Symptoms often develop gradually.
Should TSH be tested alone?
TSH is the best first screen, but if it is abnormal, clinicians usually add free T4 (and sometimes T3 and antibodies) to clarify what is happening. TSH alone tells you there is a problem, not always what kind.
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