TSH
Thyroid Stimulating Hormone
- Sample
- Blood
- Usual units
- µIU/mL
- Fasting
- No fasting is usually needed.
Also known as Thyroid Stimulating Hormone · TSH Ultrasensitive · TSH - Ultrasensitive · S. TSH · Thyrotropin
What this test measures
Thyroid-stimulating hormone is made by the pituitary gland and signals the thyroid gland to produce more or less thyroid hormone, forming a feedback loop between the two glands. A lab reads TSH as the first look at how that loop is running. A blood test measures its concentration, commonly in micro-international units per milliliter (µIU/mL).
Reading your report
There isn’t one standard range for this test — each lab prints its own. Use the range shown next to your result.
Related guides
- Guide
Why the same blood test has different "normal" ranges at different labs
Reference intervals are built from each lab's own population and equipment, which is why two labs can print different ranges for the same sample.
- Guide
Reference interval, cutoff, and the "optimal" numbers online: three different things
The range beside your result, the target a website quotes, and the threshold that defines a condition are built in different ways and answer different questions.
- Guide
Why the same lab printed a different reference range for you this year
Ranges are not fixed constants. The lab can change method, revise its reference group, or apply a range that depends on your age — none of which is an error.
- Guide
TSH, free T4 and free T3: why the first number isn't a thyroid hormone
TSH is made by the pituitary, not the thyroid, and moves opposite to the hormones it controls. What each row measures, and why free and total are different tests.
- Guide
What the H and L flags on a lab report actually assert
A flag compares your number to the range printed beside it on that page — nothing more. What it does not tell you, and why healthy people collect them.
- Guide
Panels, profiles and packages: what you actually paid for
A panel is a bundle of individual tests sold under one name, and the names are not standardised. How to work out what a package included — and what it left out.