TSI Antibodies - Kresser Institute Membership Site

Marker Name: TSI antibodies

REFERENCE RANGE FOR TSI ANTIBODY ACTIVITY:

Laboratory reference range: 0–139% of basal activity

DESCRIPTION:

TSI stands for thyroid-stimulating immunoglobulin. Unlike thyroid peroxidase or thyroglobulin, there is no biological structure called thyroid-stimulating immunoglobulin. Instead, TSI antibodies are autoantibodies that recognize and bind to epitopes on the thyroid-stimulating hormone receptor (TSHR). In general, anti-TSHR antibodies may activate, block, or have no effect on the receptor.¹ TSI antibodies, specifically, are autoantibodies that activate the TSH receptor, thereby increasing the synthesis and secretion of thyroid hormones.

TSI antibodies are not affected by the normal feedback mechanisms that regulate thyroid-releasing hormone (TRH), thyroid-stimulating hormone (TSH), and thyroid hormone levels. Increases in the thyroid hormones triiodothyronine (T3) and thyroxine (T4) would normally provide negative feedback to the hypothalamus and pituitary glands, thereby decreasing the release of TRH and TSH, respectively.^2,3 TSI antibodies, however, continue to interact with thyroid tissue independent of hormone levels.

Anti-TSHR antibodies are present in virtually every form of autoimmune thyroid condition, whether it results in hypothyroidism, hyperthyroidism, or a euthyroid state. In fact, stimulating, neutral, and inhibiting anti-TSHR antibodies may be present in the same individual (e.g., an individual with Graves’ disease).⁴ These antibodies may counteract the action of one another such that relative levels of stimulating and inhibiting antibodies may predict overall thyroid function at a given time.¹

In fact, modern tests of TSI antibodies do not necessarily detect the mere presence of TSI antibodies, but rather quantify their net activity on the TSHR. Specifically, the modern test is typically an activity assay that observes the overall effect of any stimulating, inhibitory, and neutral antibodies present.⁵

The presence of anti-TSHR antibodies and increased TSI activity indicates Graves’ disease.⁷ Testing is also used to monitor remission or relapse in patients treated for Graves’ disease.⁶ TSI antibodies may also be used to quantify risk for neonatal and/or gestational thyrotoxicosis in pregnant women with Graves’ disease.

The TSI antibodies test is typically measured after or with other thyroid function testing (e.g., TSH, total T3, free T4, TPO antibodies, Tg antibodies).

PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS:

High in:^1,5,7

Graves’ disease
Hashitoxicosis
Gestational thyrotoxicosis
Neonatal thyrotoxicosis
Silent thyroiditis

Low in:

Not applicable

FUNCTIONAL RANGE INDICATIONS:

High in:

No functional range

Low in:

No functional range

References: