Hiya Joan!
TSI is Thyroid Stimulating Immunoglobulins. It shows there is thyroid type antibodies present in the blood or something like that. It is a special test and also gives a different number (on mine) for TSH.
Once again here is some of what my lab report says regarding TSI:
“TSI are found in as many as 95% of untreated, hyperthyroid patients with graves’ and and in up to 57% of patients with euthyroid Graves’.”
The above is the extent of my not-so-vast knowledge of the subject.
Bruce