Journal of Korean Endocrine Society 1994;10(3):191-199.
Published online November 6, 2019.
Clinical Significance of Thyrotropin Measurement as a Screening Test in Ambulatory Patients.
Young Kee Shong, Hong Kyu Kim, Ghi Su Kim, Dae Hyuk Moon
Abstract
The objective of this study is to determine the clinical significance of thyrotropin(TSH) measurement as a screening test in ambulatory patients. One hundred and nintynine patients with abnormal TSH levels detected at routine examinations were studied. The patients were examined and histories about the recent medications and nonthyroidal illness were taken. Additional thyroid tests were done including measuments of total T_3, free T_4, antithyroid autoantibodies, thyroid scan and radioiodine uptake. Of the total 199 patients, 107(54.7%) had thyroid diseases. 49 out of 101 patients with subnormal TSH had thyroid diseases, and the remainder had supressed TSH due to medications, associated nonthyroidal illness, and normal variations. 58 out of 99 patients with elevated TSH had thyroid diseases. Of those 47 patients whose TSH level was below 0.05 mIU/L, functional sensitivity of TSH assay in our laboratory, 37 had thyroid diseases. Of those 19 patients whose TSH level was above 7.0mIU/L, two times of upper normal limit, all had thyroid iseases.Simultaneous measurement of free T_4 disclosed 50(25.1%) out of total 199 patients with abnormal TSH levels had abnormal free T_4 values which is regarded as evidence of clinical thyroid dysfunction. In summary, a single measurement of TSH level alone seems to have high sensitivity but low specificity. Simultaneous measurement of free T_4 can reasonably compensate the low specificity of TSH measurement. In case of ambulatory patients without significant nonthyroidal illness, TSH values below functional sensitivity or above twice upper normal limit may predict thyroid disease and dysfunction with reasonable specificity.
Key Words: TSH, free T4, Sensitivity, Specitivity


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