Insights on the production of T3 hormone and hypothyroid diagnosis

The thyroid is responsible for producing only 20% of the T3 hormone in the blood, while 80% is produced outside of the thyroid. A low T3 diagnosis of hypothyroid may not be primarily due to the thyroid, as 80% of the hormone production occurs outside the thyroid through the conversion of T4 into T3 in the gut, periphery, and liver, facilitated by nutrients like selenium and thiamine.