Quote:
mineralman - Mine only included free T3, free T4, and TSH. What extra information would the total T3 and total T4 give me?
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"When interpreting thyroid function, it is very important to obtain a Total T4.
T4 is about 98 percent of circulating thyroid hormone.
If one is treated with T3 (Liothyronine, Triiodotyronine), then Total T3 will also be important to determine what is occurring.
Thus a more complete thyroid panel would include:
Free T4, TSH
Free T3
Total T3
Total T4
One reason total values are important is that the free levels are influenced by the availability of the various thyroid binding proteins - such as albumin, thyroid binding globulin, and transthyretin.
These binding proteins are influenced by other factors, such as:
Albumin - hydration, general nutrition
Thyroid binding globulin - estrogen signaling strength
Transthyretin - vitamin A signaling strength (since it not only binds T3 preferentially but also viltamin A)
The binding protein levels are not accounted for by the free levels of T3 or T4. Thus when other factors come into play, they will directly interfere with or complicate interpretation.
Additionally, you have weakly bound versus strongly bound interactions with the binding proteins - just as Albumin vs. SHBG have weak vs. strong binding to testosterone. (This is why total testosterone is the best measure overall of testosterone signaling strength.)
Total T4 can be used as a ceiling for how much T4 can be given. Similarly with T3.
Free T4 is not a sensitive indicator of total thyroid signaling strength.
Free T3 is one indicator of total thyroid signaling strength, but I would also take into account Total T4 since thyroid can also be converted within certain cells to T3 prior to use.
Using Free T3 without a total T4 (and Total T3 if needed) to determine thyroid hormone dosing is like flying blind in fog. There is no indication of the endpoint. It would be like using Free Testosterone to determine how much testosterone to give.
In addition to lab tests, it would be important to also try to establish physical markers as targets when doing thyroid replacement therapy. This would include reduction or correction of signs of thyroid hormone deficiency. When one can establish physical markers/signs to determine thyroid dosing, it can be as sensitive or as good as lab tests. This is how physicians did it prior to the development of lab tests.
Combining both physical exam and lab testing would be ideal though patients may not have the means for frequent lab testing. Thus the choice of labs needs to be tailored to the patient and their circumstances.
Winter is a particularly stressful time. One factor is colder weather which forces an increase in sympathetic nervous system activity. This may lead to a reduction in serotonin signaling. This then may result in a reduction in thyroid hormone production. Additionally, the stress resulting from cold weather may result in adrenal fatigue, which would result in a reduction in T4 to T3 conversion. Lower vitamin D levels - as it is used up from fat stores in darker light - also may result in a reduction in serotonin signaling, resulting in a reduction in thyroid hormone production. Stress may also result in zinc loss, impairing thyroid hormone production. Stress also increase insulin resistance, leading to a renal loss of iodine, possibly impairing thyroid hormone production."
Dr. romeo