• 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 <121, three >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.
(Arch Intern Med 140:1045-1049, 1980)
dos Remedios LV, Weber PM, Feldman R, Schurr DA, Tsoi TG. Detecting Unsuspected Thyroid Dysfunction by the Free Thyroxine Index. Arch Intern Med. 1980;140(8):1045–1049. doi:10.1001/archinte.1980.00330190057019