A full thyroid panel consists of TSH, Free T4, Free T3, reverse T3, total T3, thyroid antibodies(TPO, TG). These give an in depth look at what is going on intently with your thyroid gland. There are thyroid receptors on every organ of the body and it is necessary to make sure you have enough of the active hormone getting to where it needs to go. The thyroid is the check engine light of your entire body. It regulates temperature, sleep, digestion, fertility and ovulation and a myriad of other very important mechanisms. TSH alone can not tell you what your thyroid is doing and how it is getting disbursed throughout the body. TSH is the Thyroid Stimulating Hormone and it is made in the pituitary and it is a hormone that activates when the thyroid needs more thyroid hormone. It is only helpful in a full panel of lab ranges.
Secondly, optimal lab ranges are crucial. Lab ranges are different slightly depending on the lab that actually runs the test. Also, lab ranges are compiled from an average of the population that gets those labs done. So when lab ranges are referenced by a physician or on a lab sheet they are simply there from the lab and have no indication of what is the optimal lab range for functionality of that organ or system being tested. Optimal lab ranges are usually in a smaller range, however even in a tighter range that also allows room for optimal in the many different bodies and systems that represent the population.