<p>Thyroid hormones are primarily eliminated by the kidneys. A portion of the conjugated hormone reaches the colon unchanged and is eliminated in the feces. Approximately 20% of T<sub>4</sub> is eliminated in the stool. Urinary excretion of T<sub>4</sub> decreases with age.<sup class="text-reference-group"><a class="reference-popover-link" data-content="American Association of Clinical Endocrinologists (AACE): Clinical Practice Guidelines for Hypothyroidism in Adults" href="#reference-F4636">15</a></sup></p>