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T3 Conversion Efficiency

Meaning

T3 conversion efficiency is the physiological measure of how effectively the body converts the relatively inactive thyroid prohormone, thyroxine (T4), into the highly potent, biologically active triiodothyronine (T3) at the cellular and tissue level. This process is mediated primarily by deiodinase enzymes, particularly D1 and D2, located in tissues like the liver, kidneys, and skeletal muscle. Suboptimal conversion efficiency is a common clinical finding that can lead to symptoms of hypothyroidism despite normal T4 and TSH levels, reflecting a functional impairment in thyroid hormone action.