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 reverse T3?

Reverse T3, or rT3, is an inactive form of thyroid hormone. When the body converts T4, it can produce either active T3 or inactive reverse T3. Making more reverse T3 is one way the body can effectively dial down thyroid activity, for example during illness, stress or fasting.

Why it matters

Reverse T3 is a more specialised marker, sometimes used to help understand why someone feels hypothyroid despite normal standard tests. Its interpretation is debated among clinicians, so it is best viewed as one supporting piece of a larger thyroid picture rather than a stand-alone answer.

What your results can mean

Raised

A high reverse T3 can reflect the body downshifting thyroid activity in response to illness, stress, or low energy availability. It is interpreted cautiously and always in context.

Within range

A reverse T3 in range suggests the balance between active and inactive conversion is typical, and shifts attention back to the standard thyroid markers.

Reference ranges in Australia

Reverse T3 reporting and reference ranges vary between laboratories and assays, and it is a less standardised test than TSH or free T4. Read your result against the range on your own report, and interpret it with a clinician alongside your full thyroid panel.

Test your thyroid with Precursor

Reverse T3 only makes sense within a fuller thyroid picture. At Precursor, thyroid testing is requested and reviewed by a clinician within Full Advanced Bloods, a single draw covering your thyroid, heart, metabolic, hormonal, kidney, liver and nutrient markers together, so specialised markers are read in proper context.