Endocrine Abstracts

Introduction: Anti-TSH receptors (TRAb) are an important marker in the differential diagnosis of the etiologies of hyperthyroidism. They detect serum TSH receptor immunoglobulins that interact with the TSH receptor without the functional discrimination of stimulating from blocking antibodies. A new assay has recently been released, that utilizes recombinant human TSH receptors (hTSHR) for the specific detection and quantification of thyroid stimulating autoantibodies (TSI).

Objective: To evaluate the agreement of a new TSI test by method comparison with a TRAb RIA, in the assessment of Graves disease (GD) in clinically well defined patients.

Material and methods: We studied 162 patients regularly assisted at CHLC, Lisbon: 104 clinically documented GD, 29 with other thyroid diseases and 29 with non-thyroid autoimmune disease. The serum samples were analyzed by a RiaRSR TRAb CT, traceable to WHO standard 90/672, and a new automatic chemiluminescent immunoassay, Immulite 2000 TSI (Siemens), traceable to WHO 2nd IS, NIBSC 08/204.

Results: At manufacturer TSI cut-off (0.55 IU/l), the clinical sensivity and specificity were: 97.1 and 91.4% and at TRAb cut-off (1.5 IU/l), 80.7 and 94.8% respectively. The agreement of the results in the range of 0–1.5 IU/l revealed the occurrence of 17 positive results in TSI that were negative or gray in RIA.

Conclusions: TSI may prove to be a useful method in clinical practice, by automating and discriminating the functional activity of the TRAb.The high sensitivity of TSI may be of great value in the diagnosis and follow up of GD and a good alternative to the RIA assay.