the purpose of t3 and t4 is regulation of metabolism.
what is the purpose of t3 and t4?
regulation of metabolism
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because a single abnormal tsh level can be misleading, t3 and t4 levels must be measured in the blood to further confirm the diagnosis. when circulating in the body, t3 and t4 are bound to transport proteins. only a small fraction of the circulating thyroid hormones are unbound or free, and thus biologically active. t3 and t4 levels can thus be measured as free t3 and t4, or total t3 and t4, which takes into consideration the free hormones in addition to the protein-bound hormones. free t3 and t4 measurements are important because certain drugs and illnesses can affect the concentrations of transport proteins, resulting in differing total and free thyroid hormone levels. there are differing guidelines for t3 and t4 measurements.
thyroid disease