title: Detecting unsuspected thyroid dysfunction by the free thyroxine index.
abstract: The free thyroxine index (FTI) was used in 2,704 adults to detect unsuspected thyroid dysfunction. Among 2,581 adults found to be clinically euthyroid without thyroid medication, 2,571 had a truly normal FTI (121 to 360) and ten had a falsely abnormal FTI (seven less than 121, three greater than 360). Among 25 subjects with newly diagnosed thyroid dysfunction, there were eight hyperthyroid (prevalence, 0.31%) and 14 hypothyroid (prevalence, 0.50%) subjects. The sensitivity of the FTI was 1.0, and the specificity was 0.996. The predictive value of an abnormal FTI with a prevalence of 0.81% was 67%. The cost to find a new case averaged $127. The annual incidence of symptomatic hyperthyroidism was 0.05%; of hypothyroidism, about 0.08%. We conclude that the FTI is cost-effective for case finding in thyroid dysfunction.
mesh_terms: D000368:Aged; D003365:Costs and Cost Analysis; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000175:diagnosis; D007037:Hypothyroidism / Q000175:diagnosis; D008297:Male; D008875:Middle Aged; D009098:Multiphasic Screening; D013959:Thyroid Diseases / Q000175:diagnosis* / Q000188:drug therapy; D013960:Thyroid Function Tests / Q000191:economics; D013974:Thyroxine / Q000097:blood*
chemical_list: D013974:Thyroxine