Prevalence and causes of undiagnosed hyperthyroidismin an adult healthy population. The Tromsø study.
BACKGROUND
The causes of subclinical hyperthyroidism have only been reported from clinical studies.


OBJECTIVE
To determine the prevalence and pathological causes of reduced serum TSH levels in subjects recruited from an epidemiological survey.


METHODS
Serum TSH was measured in 7954 subjects in the 5th Tromsø study. Subjects with serum TSH<0.50 mIU/l, not using T4, without a previous diagnosis of thyroid disease, without serious concomitant disease, and younger than 80 yr, were invited for a re-examination. If low serum TSH was persistent, thyroid scintigraphy was performed.


RESULTS
Among the 4962 subjects that met the inclusion criteria, serum TSH was <0.50 mIU/l in 105 subjects. Twelve subjects had a suppressed serum TSH level (<0.05 mIU/l). Two of these were lost to follow-up, 4 had Graves' disease, 4 had adenoma, and 2 had multinodular goiter. In the 93 subjects with serum TSH 0.05-0.5 mIU/l, 55 were re-examined, of whom 35 had normalized their serum TSH level. In the remaining 20 subjects, 1 had Graves' disease, 6 had adenoma (of which 2 were toxic adenomas), 7 had multinodular goiter, and 6 were considered normal. Among the 521 subjects using T4, 70 (13.4%) had a suppressed serum TSH level.


CONCLUSIONS
Most of the subjects with a suppressed serum TSH level will be on T4 medication. Otherwise, if the suppressed serum TSH level is found by chance, this probably represents a clinically important thyroid pathology. Also, in subjects with a persistently low serum TSH level (0.05-0.5 mIU/l) most will have a pathological thyroid scan.
Bjørndal
M M
MM
Institute of Clinical Medicine, University of Tromsø, Norway.
Sandmo Wilhelmsen
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Jorde
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D000236:Adenoma / Q000150:complications; D000328:Adult; D000368:Aged; D015331:Cohort Studies; D005260:Female; D006044:Goiter, Nodular / Q000150:complications; D006111:Graves Disease / Q000150:complications; D006306:Health Surveys; D006801:Humans; D006980:Hyperthyroidism / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D011877:Radionuclide Imaging; D013670:Sodium Pertechnetate Tc 99m; D013961:Thyroid Gland / Q000000981:diagnostic imaging; D013964:Thyroid Neoplasms / Q000150:complications; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000627:therapeutic use
D013972:Thyrotropin; D013670:Sodium Pertechnetate Tc 99m; D013974:Thyroxine