An epidemiological study of the serum thyrotropin reference range and factors that influence serum thyrotropin levels in iodine sufficient areas of China

The aims of this study performed in 2007 were to verify the selection criteria proposed by the National Academy of Clinical Biochemistry (NACB) guidelines, to investigate factors that influence thyrotropin (TSH) levels, and to determine serum TSH reference range in iodine sufficient areas of China. After excluding 291 subjects, a total of 5,348 inhabitants from three iodine sufficient areas of Liaoning province were asked to fulfill the questionnaire, and take TSH, thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) measurements and a thyroid ultrasound examination. The distribution of TSH was right skewed in normal people. It has been customary to log transform the values to observe the Gaussian distribution. In the subjects 12-19 years of age, the TSH level was significantly higher than in the other age groups (p<0.001), while there were no significant difference in the TSH values of the other age groups. The TSH levels in females(1.68 +/- 1.90mIU/L) were significantly higher than in males (1.45 +/- 1.92mIU/L) (p<0.001). Therefore, the normal TSH range in males over age 20 was 0.43-4.74mIU/L, and in females the range was 0.48-5.39 mIU/L. A family history of thyroid disease, abnormal thyroid ultrasound, a thyroid antibody-positive status were the factors that influenced the TSH reference range. Non-thyroid disease did not impact the TSH reference range significantly. We recommend use of a TSH reference range 0.46-5.19mIU/L in iodine sufficient areas of China for males and females over 20 years old. We suggest using a normal thyroid ultrasound as a new criterion in addition to the NACB guidelines to determine the TSH reference range.