THYROID
Free Triiodothyronine
Also known as Free T3
What it is
Free T3 is the active thyroid hormone available to tissues. The body converts T4 to T3 as needed.
Why it matters
Some patients feel poorly on levothyroxine (T4) alone because they do not convert T4 to T3 well. Free T3 tells us whether the active hormone is where it needs to be.
Range GPLX watches for
GPLX watches for Free T3 in the upper half of the lab reference in symptomatic patients. Your physician interprets alongside TSH and Free T4.
This educational range is not a personal diagnostic threshold. Your physician interprets your result in context of your full biomarker panel, medications, symptoms, and history.
What abnormal values can suggest
If low
A low Free T3 value can suggest poor T4-to-T3 conversion, severe illness, or under-replacement.
If high
A high Free T3 value can suggest hyperthyroidism, T3 supplementation, or thyroid hormone abuse.
This marker is reviewed when clinically appropriate as part of physician-directed labs. Membership is $39.99/month; consultation is $30.
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