High free T3 can be seen in early thyrotoxicosis, T3-type hyperthyroidism, hyperthyroidism crisis, etc. It can also be normal, and needs to be evaluated together with thyroid stimulating hormone, thyroid antibody and other tests. 1. Early thyrotoxicosis: free T3 is very sensitive to the diagnosis of early hyperthyroidism. If there is early or recurrent thyrotoxicosis, free T3 will rise before free T4. 2. T3-type hyperthyroidism: at this time, the level of free T3 can be significantly higher than the level of free T4. 3. Hyperthyroidism crisis: when hyperthyroidism crisis occurs, it is mainly manifested as high fever and sweating, irritability, nausea and vomiting, etc., and there are obvious abnormal increase of free T3 and free T4, and abnormal decrease of thyrotropin. The presence of high free T3 requires timely medical attention to clarify the cause of the disease and timely treatment.