Educational information only. At Precursor, blood testing is requested and reviewed by a clinician and considered alongside your history and other markers, not as a stand-alone diagnosis. Testing is performed in NATA-accredited laboratories to ISO 15189 standards.

What is TSH?

TSH, or thyroid-stimulating hormone, is made by the pituitary gland in your brain. Rather than being a thyroid hormone itself, it is the signal that tells the thyroid how much hormone to produce. Because of this, TSH acts like a thermostat: when thyroid hormone runs low, TSH rises to push production up, and when it runs high, TSH falls.

Why it matters

TSH is the single most useful first-line thyroid test, because that thermostat relationship makes it very sensitive to early changes. It is usually the starting point a clinician uses, with the actual thyroid hormones measured to build the fuller picture when TSH is unexpected.

What your results can mean

If your result is higher

A raised TSH often suggests the thyroid is underactive, with the pituitary working harder to stimulate it. It is interpreted alongside free T4 and your symptoms before any conclusion is drawn.

If your result is lower

A low TSH can suggest an overactive thyroid, where high hormone levels suppress the signal. As with a high result, it is read in context rather than alone.

Australian reporting and interpretation

TSH is reported in milli-international units per litre (mIU/L). The RCPA guide interval is 0.4 to 4.0 mIU/L and may vary by laboratory. Paediatric and pregnancy-specific intervals are different, so use the range printed on your own report and review it with a clinician.

Test your thyroid with Precursor

TSH is best read alongside your thyroid hormones. At Precursor it is measured as part of Full Advanced Bloods, a single clinician-reviewed blood draw covering your thyroid, heart, metabolic, hormonal, kidney, liver and nutrient markers together, giving you and your clinician a complete thyroid picture and a baseline to track.