{"id":"thyroid-stimulating-immunoglobulin","name":"Thyroid Stimulating Immunoglobulin (TSI)","shortName":"TSI","aliases":["Thyroid Stimulating Immunoglobulin","TSI","TSI Index","Thyrotropin Receptor Stimulating Ab","Thyroid Stimulating Immunoglobulins","TSAb","Thyroid Stim Immunoglobulin","Thyrotropin Stimulating Ig","Thyroid-stimulating Immunoglobulin (TSI)","Thyroid Stimulating Immunoglobulin, Serum","Thyrotropin Receptor Stimulating Antibody"],"abbreviations":["TSI","TSAb"],"loinc":[{"code":"30567-2","primary":true},{"code":"17708-9","primary":false}],"specimen":"serum","units":[{"ucum":"[IU]/L","display":"IU/L"}],"referenceRanges":[{"population":"Adults","low":0,"high":0.55,"unit":"[IU]/L","unitDisplay":"IU/L","note":"Labcorp prints 0.00 to 0.55 IU/L for the Siemens IMMULITE 2000 TSI assay (a bridging immunoassay). The manufacturer's cutoff, as quoted by Nelson 2025, is 0.54 IU/L or less for a negative result. At 0.55 IU/L the validation study reported 98.6% sensitivity and 98.5% specificity for Graves' disease, and the highest result in 404 people with other thyroid or autoimmune diseases was 0.39 IU/L. TSI is also reported as a percentage of a reference sample's activity by cell-based bioassays (one reference laboratory's negative cutoff is 122% or less). Those results are NOT interchangeable with IU/L and cannot be converted, so they are not entered here. Use the cutoff and flag printed on your own report.","sources":[{"title":"Thyroid Stimulating Immunoglobulin (TSI) (test 140749)","url":"https://www.labcorp.com/tests/140749/thyroid-stimulating-immunoglobulin-tsi","publisher":"Labcorp"},{"title":"Thyroid-stimulating Immunoglobulin (TSI) (FFTSI)","url":"https://www.testcatalog.org/show/FFTSI","publisher":"LabCorp Burlington (Extended Catalog)"},{"title":"TSH Receptor Antibody Test Utilization Patterns From a National Reference Laboratory: TRAb, TSI, or Both?","url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC12712957/","publisher":"Journal of Clinical Endocrinology & Metabolism","year":2025}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"Antibodies that stimulate the thyroid by acting like TSH. A positive result is strongly linked to Graves' disease.","url":"https://bloodtesttracker.com/markers/thyroid-stimulating-immunoglobulin","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}