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Free T3 Bioactivity

Meaning

Free T3 Bioactivity denotes the concentration and functional effectiveness of the unbound, biologically active form of triiodothyronine (T3) at the cellular receptor level, which is the principal mediator of thyroid hormone action. This metric is considered a more precise clinical indicator of tissue-level thyroid status than total or even free T4 measurements, as T3 directly regulates basal metabolic rate, protein synthesis, and sensitivity to catecholamines. Optimal Free T3 Bioactivity is crucial for maintaining energy homeostasis and thermoregulation across all organ systems.