RESUMEN
OBJECTIVES: We conducted a study to investigate the normal range for TSH and within-individual variations of TSH according to temperature and aging. PATIENTS AND METHODS: We enrolled patients who underwent periodic medical examinations five times over a six year period (2007.8~2013.6). Anthropometric data and thyroid ultrasonography were evaluated, and serum TSH, T3, and T4 were assayed. RESULTS: Subjects were 19-64 years old, 120 were female, and 208 were male. Reference ranges for TSH were 0.53-4.94 mIU/L in the first test, 0.49-5.61 mIU/L in the second test, 0.46-6.06 mIU/L in the third test, 0.48-5.99 mIU/L in the fourth test, and 0.52-6.3 mIU/L in the fifth test. When the TSH level was analyzed according to temperature and sex, mean TSH was higher in months in which the average monthly temperatures were below 10degrees C in Jinju, Gyeongnam and female. The aging and low temperatures are associated with increased serum TSH concentrations in the within-individual. CONCLUSIONS: This study showed that aging is associated with increased serum TSH concentrations in the within-individual and serum TSH concentrations are different in the within-individual according to the temperature.