Measuring T3 is important because it is the biologically active thyroid hormone.

“and releases T4 and T3 and guess what you can basically forget about T4 T4 it's not completely inactive it has some roles but T3 is the one that's more or less active”

“at the end of the day the only biologically active thyroid hormone is t3 okay that's just the bottom line t4 is a storage hormone nothing wrong with that it's supposed to be there”

“T3 is the generally accepted to be the active form of thyroid hormone.”

“We're talking about the other hormone, the active hormone, T3. So, it's amazing that by just removing one atom of iodine from the T4, it now becomes a fully active hormone.”

“Why would you measure T3? I mean why would you not measure T3? It's the biologically active hormone.”

“T3 is the biological reactive hormone.”