The changes of thyrotropin level in euthyroid population:a 5-year follow-up study in communities with different iodine intakes / 中华内科杂志

ABSTRACT

Objective To determine the factors that influence the development of abnormal thyrotropin (TSH) level in an euthyroid population.Methods We conducted a follow-up study in 3 communities with different iodine status.Of the 3403 euthyroid subjects at baseline screened in 1999,80.1% ( n = 2727 ) was visited and sampled in 2004 for measuring TSH,thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb).Results Iodine status in the 3 communities were stable.Decreased TSH level( <0.3 mU/L) developed in 2.5% (n =68) of sampled subjects,while raised TSH level( > 4.8 mU/L) in 2.4% (n = 64).A logistic analysis showed that risk factors for developing decreased TSH level included positive conversion of TPOAb (OR = 5.5 ),positive TPOAb both in 1999 and in 2004 ( OR = 4.0),positive TgAb in 2004 ( OR = 3.7) and TSH < 1.0 mU/L in 1999 ( OR = 2.6).Risk factors involved in developing raised TSH level included iodine status of Zhangwu community ( OR = 4.1 ),iodine status of Huanghua community ( OR = 3.9),positive TgAb in 2004 ( OR = 3.7 ),positive TPOAb both in 1999 and 2004 (OR =3.6),positive conversion of TPOAb (OR =2.7) and TSH > 1.9 mU/L in 1999 (OR = 2.6 ).Conclusions Exposure to long-term iodine excess imposes danger of developing hypothyroidism.The risk will be even higher when exposing to iodine adequacy after correction of iodine deficiency.An interval between 1.0 and 1.9 mU/L of TSH level was optimul with the least probability of developing abnormal TSH level.