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 was examined and histories about the recent medications and nonthyroidal illness were taken. Additional thyroid tests were done including measurements of total T3, free T4, antithyroid autoantibodies, thyroid scan and radioiodine
uptake.
Of the total 199 patients, 107(54.7%) had thyroid disease. 49 out of 101 patients with subnormal TSH had thyroid diseases, and the reaminder 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 diseases.
Simultaneous measurement of free T4 disclosed 50(25.1%) out of total 199 patients with abnormal TSH levels had abnormal free T4 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 T4 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(J Kor Soc Endocrinol 10:191~199, 1995).
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