Factitious Elevation of Thyrotropin in Euthyroid Patients

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Abstract
To the Editor: Elevation of the serum concentration of thyroid-stimulating hormone (TSH) is a sensitive indicator of primary hypothyroidism. Reports from European centers have shown that heterophilic antibodies neutralizing the rabbit antihuman TSH serum of conventional TSH assays cause falsely high TSH levels.1 2 3 4 In 1983 we reported on a patient with falsely elevated TSH levels.5 We saw an additional five patients with falsely elevated TSH levels between March and November of 1984, when 7824 patients had TSH assays in our office. There were elevated TSH levels in 675 patients, of whom 376 had subnormal free thyroxine indexes. Elevated TSH levels . . .