TSH Receptor Antibody Test Utilization Patterns from a National Reference Laboratory: TRAb, TSI, or Both?

Abstract

Background: There are currently two classes of thyroid stimulating hormone receptor (TSHR) antibody assays, namely TSHR antibody (TRAb) assays and thyroid stimulating immunoglobulin (TSI) assays. Clinical guidelines do not currently specify appropriate use of TSHR autoantibody tests in the diagnosis of hyperthyroidism which may result in paired orders for both tests with the possibility of discordant results and excessive costs.

Methods: Over 189,000 patient encounters with TRAb and TSI bioassay (TSI-BA) or TSI bridge immunoassay (TSI-Br) test orders were examined to assess the frequency of paired orders and qualitative agreement of TRAB/TSI. A chart review was performed on a subset of patients for clinical correlation. Lastly, a cost analysis was performed to estimate the financial burden of unnecessary paired testing.

Results: TRAb and TSI were co-ordered on the same encounter in 14.3% of TRAb/TSI-BA orders and 17.4% of TRAb/TSI-Br orders. Qualitative comparison showed discordance in 12.5% (1,590) of TRAb and TSI-BA paired orders and 6.6% (1,149) of TRAb and TSI-Br paired orders. Based on patient FT4 and TSH concentrations and disease status, the TSI assays aligned better with hyperthyroidism and confirmed Graves' disease diagnoses. Paired orders resulted in a 31-325% increase in potentially unnecessary testing costs.

Conclusions: We observed good clinical and analytical agreement between TRAb and TSI assays suggesting that paired orders for TRAb and TSI are redundant in the assessment of autoimmune-mediated hyperthyroidism. Use of a single test to assess TRAb would be appropriate in most scenarios and may lead to considerable savings of healthcare dollars.