TSH
Also written as: Thyroid stimulating hormone
The pituitary signal that tells the thyroid to work harder.
What it measures
Thyroid stimulating hormone, produced by the pituitary gland. It is not a thyroid hormone itself - it is the instruction the brain sends to the thyroid, which is why it moves in the opposite direction to thyroid activity.
Why a doctor orders it
It is the usual first-line thyroid test, and it is monitored when someone takes thyroid hormone replacement.
What is generally associated with a higher result
A higher TSH means the pituitary is signalling harder, which is broadly associated with an underactive thyroid. It can also rise temporarily while recovering from illness.
What is generally associated with a lower result
A lower TSH is broadly associated with an overactive thyroid, and with taking more thyroid hormone replacement than the body needs.
Everyday things that move this number
Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:
- Time of day - TSH is typically higher overnight and early morning
- Recent acute illness
- Biotin supplements, which interfere with many thyroid assays
- Pregnancy, which shifts the expected range
Questions to take to your appointment
- Should free T4 be checked alongside this?
- Do I take biotin, and could it have affected this result?
Build a printable questionnaire with your own results →
Where to read more
MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .
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