成人甲状腺功能减低(甲减)按病因分原发性甲减和继发性甲减两类。后者包括下丘脑TRH缺乏所致的所谓第三性甲减。按其临床表现又可分为亚临床型甲减与临床甲减两型。前者多属早期轻症,由于TSH代偿性分泌增加,病人一般无甲减的症状和体征,甚至T_4亦在正常范围而只有TSH增高,后者由于失代偿,甲状腺激素水平低下,通常T_4.<3～4μg/dl时临床出现甲减症状和体征,如疲乏无力、怕冷、 Adult hypothyroidism (hypothyroidism) by the cause of primary hypothyroidism and secondary hypothyroidism two categories. The latter include the so-called third hypothyroidism caused by a lack of TRH in the hypothalamus. According to their clinical manifestations can be divided into subclinical hypothyroidism and clinical hypothyroidism two types. Most of the former are mild early, due to TSH compensatory secretion increased, patients generally without hypothyroidism symptoms and signs, and even T_4 also in the normal range and only TSH increased, which due to decompensation, thyroid hormone levels are low, usually T_4 <3 ~ 4μg / dl clinical symptoms and signs of hypothyroidism, such as fatigue, weakness, cold,