What is the difference between thyroid profile total and thyroid profile free?
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Answer:
About 95% of thyroid hormone is bound to plasma proteins - thyroid binding globulin (TBG), constituting 'total thyroid hormone'. The remainder, approximately 5%, is 'free' in the circulation and therefore metabolically active. It's worth noting that T4 is a pro-hormone, which is converted into T3 by 5'-iodinase. T3 has a higher metabolic activity than T4, but has a shorter half-life. Taking this into account, I would say free T4 (FT4) is a good assessment of thyroid hormone levels. It would also be worth testing FT3, given that there can be issues in the conversion of T4 to T3. It may also be worth testing for thyroid stimulating hormone (TSH), which if elevated, along with a depressed FT4 result, is indicative of hypothyroidism.
T4 is thyroid
and FT4 is free thyroid