CONTEXT: The widespread use of thyroid tests in asymptomatic individuals identifies many patients with transient subclinical hypothyroidism. OBJECTIVE: Our objective was to determine the effect of seasonal change on serum TSH levels and the transition between subclinical hypothyroid and euthyroid status. DESIGN, SETTING, AND SUBJECTS: This was a retrospective longitudinal study of 1751 subclinical hypothyroid and 28 096 euthyroid subjects aged over 18 years who underwent serial thyroid function tests at a health screening center between October 2003 and May 2011. MAIN OUTCOME MEASURES: Age-adjusted geometric mean values of the TSH level by month were calculated using linear mixed models. Adjusted odds ratios of test season and multiple baseline clinical factors were determined using generalized estimating equations. RESULTS: During a median 36 months of follow-up, 57.9% of subclinical hypothyroid subjects reverted to euthyroidism, and 4.3% of euthyroid subjects developed subclinical hypothyroidism. The monthly distribution of follow-up TSH levels indicated a biphasic pattern, ie, an increase during the winter-spring season and a decrease during the summer-fall season, with a maximal TSH difference of 0.69 mIU/L in subclinical hypothyroid and 0.30 mIU/L in euthyroid subjects. Normalization of subclinical hypothyroidism was increased 1.4-fold in follow-up tests during the summer-fall follow-up, whereas subclinical hypothyroidism increased 1.4-fold in euthyroid subjects during the winter-spring follow-up. CONCLUSIONS: The season in which thyroid testing was performed was independently related to the transition between subclinical hypothyroid and euthyroid status. Seasonal variations in TSH concentration should be considered before deciding on treatment of subclinical hypothyroidism, particularly in the areas with a wide annual temperature range.
CONTEXT: The widespread use of thyroid tests in asymptomatic individuals identifies many patients with transient subclinical hypothyroidism. OBJECTIVE: Our objective was to determine the effect of seasonal change on serum TSH levels and the transition between subclinical hypothyroid and euthyroid status. DESIGN, SETTING, AND SUBJECTS: This was a retrospective longitudinal study of 1751 subclinical hypothyroid and 28 096 euthyroid subjects aged over 18 years who underwent serial thyroid function tests at a health screening center between October 2003 and May 2011. MAIN OUTCOME MEASURES: Age-adjusted geometric mean values of the TSH level by month were calculated using linear mixed models. Adjusted odds ratios of test season and multiple baseline clinical factors were determined using generalized estimating equations. RESULTS: During a median 36 months of follow-up, 57.9% of subclinical hypothyroid subjects reverted to euthyroidism, and 4.3% of euthyroid subjects developed subclinical hypothyroidism. The monthly distribution of follow-up TSH levels indicated a biphasic pattern, ie, an increase during the winter-spring season and a decrease during the summer-fall season, with a maximal TSH difference of 0.69 mIU/L in subclinical hypothyroid and 0.30 mIU/L in euthyroid subjects. Normalization of subclinical hypothyroidism was increased 1.4-fold in follow-up tests during the summer-fall follow-up, whereas subclinical hypothyroidism increased 1.4-fold in euthyroid subjects during the winter-spring follow-up. CONCLUSIONS: The season in which thyroid testing was performed was independently related to the transition between subclinical hypothyroid and euthyroid status. Seasonal variations in TSH concentration should be considered before deciding on treatment of subclinical hypothyroidism, particularly in the areas with a wide annual temperature range.
Authors: Lesley Roberts; Deborah McCahon; Oliver Johnson; M Sayeed Haque; James Parle; Fd Richard Hobbs Journal: Br J Gen Pract Date: 2018-08-28 Impact factor: 5.386
Authors: So Yoon Choi; Dae Yong Yi; Soon Chul Kim; Ben Kang; Byung Ho Choe; Yoon Lee; Yoo Min Lee; Eun Hye Lee; Hyo Jeong Jang; You Jin Choi; Hyun Jin Kim Journal: J Korean Med Sci Date: 2021-05-24 Impact factor: 2.153
Authors: Tae Hyuk Kim; Ji Young Joung; Mira Kang; Sun Kyu Choi; Kyunga Kim; Ju Young Jang; Yoon Young Cho; Yong-Ki Min; Jae Hoon Chung; Sun Wook Kim Journal: PLoS One Date: 2015-12-17 Impact factor: 3.240