TSH (thyroid-stimulating hormone)
TSH, thyroid-stimulating hormone, is a pituitary hormone that controls the thyroid gland. It is usually the first test used to check how the thyroid is working.
At a glance
- Sample
- Blood
- Units
- mIU/L or µIU/mL: the same number
- Often looked at with
- Free T4, Free T3
- Preparation
- No special preparation is usually needed. If other tests are done from the same sample, you may be asked to come fasting.
Units
Labs print TSH in mIU/L, mU/L or µIU/mL. A thousandth of a unit per litre is a millionth of a unit per millilitre, so all three give the same number: there is nothing to convert.
Why lab ranges differ
Each lab sets its reference range for its own method and analyser, and many ranges differ by age and sex. Two labs can print different ranges for the same blood, so a result is read against the range on its own report, not against a number from another lab or a website.
Soma charts every TSH result against the range printed by the lab that measured it.
What can affect the result
- Biotin in supplements (often in hair vitamins): can give a falsely low result.
- Time of day: higher at night and early in the morning.
- A recent severe illness.
If something like this applies, mention it to the doctor who reads your results.
Questions
Why does my lab’s TSH range differ from another lab’s?
Each lab sets its range for its own method and equipment, and many ranges differ by age and sex. That’s why a result is best read against the range printed on the same report.
How do I prepare for a TSH test?
No special preparation is usually needed. If other tests are done from the same sample, you may be asked to come fasting. Follow your lab’s instructions.
Related tests
Got a lab report with TSH?
Share it to Soma: it reads every row on your phone, with no account and no upload, and puts your TSH on one chart with your earlier results, each against the range your lab printed.
Sources
- TSH (Thyroid-stimulating hormone) Test — MedlinePlus, U.S. National Library of Medicine.
Mention of a source doesn’t mean it endorses Soma. This page explains the test; it doesn’t diagnose and is not medical advice. Talk to your doctor about what your results mean.