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 free T3?
Free T3, or free triiodothyronine, is the most active thyroid hormone. Much of it is made when the body converts T4 into T3 in the tissues, and it is this hormone that does most of the direct work on your metabolism. As with T4, the 'free' fraction is the portion available to act, which is why it is measured rather than the total.
Why it matters
Because T3 is the more active hormone, free T3 can add detail that TSH and free T4 miss, particularly in understanding how well the body is converting and using thyroid hormone. It is generally read as part of a fuller thyroid panel rather than as a first-line test on its own.
What your results can mean
Higher than optimal
A high free T3 can accompany an overactive thyroid and is interpreted alongside TSH and free T4 to build the overall picture.
Lower than optimal
A low free T3 can occur in an underactive thyroid, and can also reflect illness or the body dialling down conversion. Context is essential, which is why a clinician reads it rather than the number alone.
Reference ranges in Australia
Free T3 is reported in picomoles per litre (pmol/L). As a general guide, many Australian laboratories use a reference interval in the region of 3.5 to 6.0 pmol/L, though ranges vary by assay. Read your result against the range on your own report and alongside your other thyroid markers.
Test your thyroid with Precursor
Free T3 adds depth to a thyroid panel. 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.
