This is a test that is rarely conducted by doctors, and even then usually only on hyperthyroid patients. However it can give a useful insight into the overall function of the thyroid. T3 is produced when TSH stimulates the thyroid. When used in conjunction with the other thyroid tests, this helps to give a complete picture of why the thyroid is underperforming. Optimal values should be somewhere in the 300-450 pg/ml range. However, the typical lab range allows values as low as 230 pg/ml.
There’s no science to back it up. The Endocrine Society, the world's largest organization of endocrinologists (people who research and treat patients with diseases related to glands and hormones), flatly says that adrenal fatigue is not a real disease. And it says the symptoms of adrenal fatigue are so general, they can apply to many diseases or conditions (depression, sleep apnea, fibromyalgia) or stem from everyday life.