Question: what is the difference between t3 and t4 thyroid tests?
Answer: T3 makes up less than 10% of what we call thyroid hormone, while T4 makes up the rest. T3, however, is about four times as strong as T4, and is thought to cause most, if not all, the effects of thyroid hormones. Many of your body's cells can turn T4 into T3; T4 may be mainly a "reservoir" used to make T3 available.