Effect of sampling time on estimates of thyroid-stimulating hormone, free thyroxine, and free triiodothyronine levels

Abstract

Despite the need for precise measurement of thyroid hormones levels for disease detection and monitoring, the importance of sampling time for the accuracy of widely used assays is unclear. In this study, the effects of the time of day on thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) levels were retrospectively evaluated using data obtained from the Laboratory Information System of Peking Union Medical College Hospital. TSH concentrations were significantly lower, and FT4 and FT3 concentrations were higher in males than in females (all p < .05). TSH decreased from 7 am to 1 pm and increased from 1 pm to 4 pm. FT3 concentrations differed among sampling time groups (p < .05). Compared to those at 7 am, the deviations in TSH, FT4, and FT3 were –24.53% to –7.41%, –0.84% to 0.84%, and –0.66% to 0.33%, respectively. TSH levels fluctuated during the day but FT4, FT3 did not exhibit a circadian rhythm. The time of sample collection must be standardized for TSH measurements.

Keywords:

• Thyroid-stimulating hormone
• free thyroxine
• free triiodothyronine
• sampling time

Acknowledgements

The authors are grateful to Siemens (China) Co., Ltd., for providing technical support. The authors also thank Wei Yu and Ling Mei from Siemens Inc. for their kind cooperation.

Ethical approval

This study was approved by the Ethics Committee of Peking Union Medical College Hospital of the Chinese Academy of Medical Sciences (SK441).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by research grants from the National Natural Science Foundation of China under [Grant number 81702060] (http://www.nsfc.gov.cn/).