Are porcine and human TSH receptor antibody measurements comparable

BACKGROUND: The human TSH receptor antibody (TRAb) assay is reported to show higher sensitivity in comparison to the "classical" porcine TRAb testing. This claim is based on studies comparing porcine TSH receptor (TSH-R) in one type of assay system (non-immobilized TSH-R and PEG to separate bound and free) with recombinant human TSH-R in another type of assay system (TSH-R immobilized on plastic tubes). In this study isotopic TRAb assays both based on the "coated tube" system (second generation) were compared for the first time. MATERIALS AND METHODS: Three hundred and nineteen consecutive undiagnosed patients from Mainz University as well as 72 patients from Dresden University with known Graves' disease were tested in the human TRAb assay and in the porcine TRAb assay. Spearman's coefficient of rank correlation and Chi-square test statistical analysis was performed. RESULTS: In the 319 consecutive patients 35 patients (11.0%) were found positive in the human assay and 36 patients (11.3%) were positive in the porcine assay. Seventy patients with Graves' disease from Dresden were positive in the assay using the porcine TSH-R and 71 out of 72 patients showed positive results in the assay with the recombinant human TSH-R. The Spearman's coefficient of rank correlation for both patient cohorts was r = 0.932 and r = 0.891 (p < 0.001), respectively. There was no significant difference in the clinical assessment regarding the diagnosis of Graves' disease. CONCLUSION: There is no clinically relevant difference in isotopic TRAb second generation assays--independent of the TSH-R used. Both TSH-R assays showed nearly similar TRAb results in consecutive samples as well as in serum samples from patients with Graves' disease.