Routine thyroid function tests as a case-finding tool.
A comprehensive, multiphasic blood panel was used as a case-finding tool for 738 patients. The thyroid function tests T4 (total thyroxine), rT3U (resin T3 uptake), and FTI (free thyroxine index) were included in this panel. Among the 711 patients found to be clinically euthyroid without known thyroid disorder, 54 had at least one abnormal parameter. Of these patients, four new diagnoses of thyroid dysfunction were made. All four cases had an abnormal T4 and FTI. Two patients had a slightly elevated FTI and normal T4, and have remained clinically euthyroid. All other patients had a normal FTI, and no thyroid dysfunction was noted. This gives FTI in this study a sensitivity of 1.0 and specificity of 0.993, which is camparable to what others have found (1). The prevalence of unsuspected thyroid dysfunction was 0.56 per cent, again comparable to other studies (1-3). It would seem the high sensitivity/specificity of FTI offsets the relatively low prevalence of unsuspected thyroid dysfunction. Since FTI is a sensitive predictor of thyroid dysfunction, consideration should be given to the inclusion of thyroid function studies in existing multiphasic case-finding panels.