Thyroid
TSH
LOINC 3016-3 · mUI/L
Ranges
Reference range: 0.4–4 mUI/L
What it is
TSH (thyroid-stimulating hormone) is made by the pituitary gland to tell the thyroid how much hormone to produce.
Why it matters
It is the first-line test of thyroid function, sensitive to even small thyroid imbalances.
What high values can mean
A higher value usually means the thyroid is underactive, so the pituitary is pushing it to work harder.
What low values can mean
A lower value usually means the thyroid is overactive, so the pituitary eases off.
How to improve it
Thyroid balance is managed medically; consistent treatment and follow-up bring TSH into range.
Food & lifestyle
Adequate iodine and selenium support the thyroid, but medication and dosing are guided by your clinician.
Preparing for the test
A blood test; fasting is not required, though testing at a consistent time can help comparisons.
When to talk to a doctor
Discuss an abnormal TSH with a doctor, who may add Free T4 and antibodies.
Related markers
Sources
- MedlinePlus (NIH)
- Testing.com (AACC)
Content reviewed on June 26, 2026
Medical disclaimer
This content is for educational purposes only. It is not medical advice and does not diagnose, treat, or prevent any condition. Reference ranges vary between laboratories — always use the range printed on your report and discuss your results with a healthcare professional.
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