A systematic review 1 included 2 studies with a total of 1 580 subjects in the first study. The second study was a follow-up study of the first. A second-generation TSH assay with a functional lower limit of 0.1 showed a LR for hyperthyroid results of 7.7 for TSH <0.1, and a LR of 0 for TSH > 0.1 to 6.6. The hypothyroid results were a LR of 0 for TSH 0.6 to 6.7, a LR of 0.74 for TSH > 6.7 to 20, and a LR of 11.1 for TSH > 20 µIU/ml. In the follow-up study using a third generation TSH assay, of the patients who truly had hyperthyroidism, 22 of 23 had a TSH level of less than 0.01.
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