Abstract. The central role of Thyroid Stimulating Immunoglobulins (TSI) in the pathogenesis of the hyperthyroidism of Graves' disease has become generally accepted and a wide variety of assays for the detection of these antibodies has been developed. The dependence on the availability of human thyroid tissue makes most of these assays unsuitable for routine clinical use, a problem circumvented by the use of nonhuman thyroid tissue in some TSI assays. We therefore compared porcine and human thyroid tissue in a TSI assay based on in vitro cAMP generation. No major differences in within and between run variation were found and, with some notable exceptions, a reasonable correlation could be demonstrated between the results in both assays (R = 0.89, P < 0.001). However, the sensitivity of the porcine TSI assay is only 60% of the estimated sensitivity of the human TSI assay. In spite of the practical advantages this porcine TSI assay, and possibly also other TSI assays using non-human thyroid tissue, cannot totally replace human TSI assays. The value of these assays in predicting the outcome of medical treatment of Graves' disease remains to be established.
