Seasonal variation of serum TSH,TT3,TT4 in normal population in Hefei

Objective To explore the seasonal changes of serum thyroid stimulating hormone(TSH), serum triiodothyronine(TT3) and serum total thyroxine(TT4) concentrations using big data obtained from the physical examination center. Methods Information of 19 434 individuals(aged>20 years) undergoing physical examination in the First Affiliated Hospital of Anhui Medical University from June 2017 to May 2019 were collected. Thyroid hormone of these subjects were detected. According to the definition of meteorological seasons, spring, summer, autumn and winter were respectively from march to May, June to August, September to November and December to February. There were 5 182 cases in spring, 5 384 cases in summer, 6 500 cases in autumn, and 2 368 cases in winter. The concentrations of TSH, TT3 and TT4 in different seasons were compared. The Spearman correlation analysis of daily TSH, TT3 and TT4 concentrations with daily maximum temperature, minimum temperature, average temperature, sunshine duration and precipitation were performed. Results Serum TSH concentration showed seasonal changes during the two years, with statistically significant difference(P<0.05). They increased in winter(2.300 μIU/mL)and spring(2.316 μIU/mL), while they decreased in summer and autumn(2.200 μIU/mL). The TT3 level was different in the four seasons, and the difference was statistically significant(P<0.05), with the highest TT3 level in autumn(1.89 nmol/L), the TT3 level in winter(1.88 nmol/L) was next. The TT4 levels in spring and summer were significantly different from those in other seasons(P<0.05), TT4 level in autumn(97.44 nmol/L) and winter(96.18 nmol/L) was the highest,and TT4 level in spring(95.76 nmol/L) was higher than that in summer(95.74 nmol/L). Spearman correlation analysis of daily TSH, TT3 and TT4 concentrations and related indicators showed that the correlation coefficients were all small, with no statistical significance(P>0.05). Conclusion The serum TSH, TT3 and TT4 concentration were significantly affected by season. The effect of seasonal change on serum TSH, TT3 and TT4 level should be considered when interpreting the results of thyroid hormone level in clinic.