THYROID
Free Thyroxine
Also known as Free T4
What it is
Free T4 is the unbound form of thyroxine circulating in the blood. T4 is the storage form of thyroid hormone that the body converts to active T3 in tissues.
Why it matters
Free T4 confirms whether the thyroid gland is producing enough hormone. It shifts before TSH does in early thyroid disease.
Range GPLX watches for
GPLX watches for Free T4 in the mid-to-upper range of the lab reference in symptomatic patients. Interpretation always sits alongside TSH and Free T3.
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 T4 value can suggest hypothyroidism, pituitary dysfunction, or severe illness.
If high
A high Free T4 value can suggest hyperthyroidism, thyroiditis, or overtreatment with thyroid hormone.
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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