Surks Martin I, Goswami Gayotri, Daniels Gilbert H
Division of Endocrinology and Metabolism, Department of Medicine, Montefiore Medical Center, 111 East 210th Street, Bronx, New York 10467, USA.
J Clin Endocrinol Metab. 2005 Sep;90(9):5489-96. doi: 10.1210/jc.2005-0170.
Recent recommendations to decrease the upper limit of the TSH reference range from 4.5 to 2.5 mIU/liter, based on the high proportion of normal people whose serum TSH is less than 2.5 mIU/liter and the observation that those with TSH between 2.5 and 4.5 mIU/liter [upper reference range (URR)] have increased risk of progression to overt hypothyroidism (Whickham, 20-yr data), have not been subjected to critical analysis.
The study subjects were from the Reference Group of NHANES III, 14,333 people more than 12 yr old, without known thyroid disease or antithyroid antibodies; 85% had TSH levels below 2.5 mIU/liter, and 2.3% had subclinical hypothyroidism (SCH). An additional 9.7% had URR TSH, representing 20.6 million Americans, who would also be identified as SCH if the upper TSH limit were decreased. Many with URR TSH do not have thyroid disease.
The time of phlebotomy is important, because the TSH level varies throughout the day, with early morning values greater than later ones, and is accentuated by sleep deprivation, strenuous exercise, or working during the night or evening shifts. Repeated measurements in the same individual vary considerably over months.
About half of those with URR TSH probably have thyroid disease, but most with thyroid disease, antithyroid peroxidase antibodies, have TSH below 2.5 mIU/liter. Those with URR TSH with thyroid disease probably have minimal thyroid deficiency, without any reported adverse health consequences or benefit of treatments with levothyroxine.
Because routine levothyroxine treatment is not recommended for SCH, it is certainly not warranted in individuals with URR TSH. For all patients with URR TSH, it is reasonable to determine serum TSH every 1-2 yr.
近期有建议将促甲状腺激素（TSH）参考范围的上限从4.5降低至2.5 mIU/升，这是基于血清TSH低于2.5 mIU/升的正常人群比例较高，以及观察到TSH在2.5至4.5 mIU/升[参考范围上限（URR）]之间的人群进展为显性甲状腺功能减退的风险增加（惠克姆，20年数据），但这些建议尚未经过严格分析。
研究对象来自美国国家健康与营养检查调查（NHANES）III参考组，14333名12岁以上、无已知甲状腺疾病或抗甲状腺抗体的人群；85%的人TSH水平低于2.5 mIU/升，2.3%的人患有亚临床甲状腺功能减退（SCH）。另外9.7%的人TSH处于参考范围上限，代表2060万美国人，如果TSH上限降低，他们也会被认定为SCH。许多TSH处于参考范围上限的人并没有甲状腺疾病。
采血时间很重要，因为TSH水平在一天中会有所变化，清晨的值高于晚些时候的值，睡眠不足、剧烈运动或夜间或晚班工作会使其更加明显。同一个体在几个月内的重复测量结果差异很大。
TSH处于参考范围上限的人群中约有一半可能患有甲状腺疾病，但大多数患有甲状腺疾病且有抗甲状腺过氧化物酶抗体的人，TSH低于2.5 mIU/升。TSH处于参考范围上限且患有甲状腺疾病的人可能甲状腺功能仅有轻微减退，没有任何已报道的不良健康后果，也没有使用左甲状腺素治疗的益处。
由于不建议对亚临床甲状腺功能减退进行常规左甲状腺素治疗，对于TSH处于参考范围上限的个体当然也没有必要。对于所有TSH处于参考范围上限的患者，每1 - 2年测定一次血清TSH是合理的。
