Anti-thyroid stimulating hormone (TSH) receptor antibodies (TRAb) exist as both stimulating and blocking antibodies. The current TRAb assays widely available to clinicians are receptor-binding assays. Bioassays that differentiate between stimulating and blocking TRAb are technically challenging and expensive. The terminology used to describe the different assays is confusing and a potential source of misinterpretation of TRAb results. In this article, we point out a typographical error in the 2011 American Thyroid Association and American Association of Clinical Endocrinologists' Guidelines on Hyperthyroidism where the term thyroid stimulating immunoglobulin (TSI) instead of thyroid binding inhibition immunoglobulin (TBII) was used in the description of TRAb results, to highlight the need to harmonize the terminology of TRAb assays to improve patient care.