The main reason for low free T3 is to look at the overall nail function, what does nail function include, free T3, free T4 and TSH, as well as thyroid peroxidase antibodies and thyroglobulin antibodies. If everything else is normal, but only free T3 is low, we need to see if the patient’s condition is not good recently, such as cold and fever, pneumonia, high blood sugar, diarrhea, nausea, vomiting, acute myocardial infarction, acute cerebrovascular disease, or acute traumatic stress disease with recent surgical consumption. If this is the case, it is called hypo-T3emia, this is a physiological phenomenon, do not care about it, until the disease recovery it will naturally recover. In fact, it is a way for the body to protect the energy supply of important organs of the body by reducing its own metabolism, do not pay too much attention to it.