Erroneous thyroid-stimulating hormone radioimmunoassay results due to interfering antibovine thyroid-stimulating hormone antibodies.

Apparent elevation of serum thyroid-stimulating hormone (TSH) levels was found in a case of a patient receiving adequate replacement therapy after thyroidectomy for a follicular carcinoma. This was an artifact due to interference with the radioimmunoassay by circulating antibovine TSH antibodies. The double-antibody technic showed spuriously elevated levels, and the single-antibody technic showed low levels of serum TSH by radioimmunoassay in the presence of antibodies.