Laboratory Services

Thyroid-Stimulating Immunoglobulin, Serum

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Updated Test Information:

Test Description
Thyroid-Stimulating Immunoglobulin, Serum

Autoimmune Thyroid Stimulator; Graves Disease; LATS (Long-Acting Thyroid Stimulator); Long-Acting Thyroid Stimulator (LATS); TSH Receptor Binding Inhibitory Immunoglobulin; TSI (Thyroid-Stimulating Immunoglobulin); Thyretain; Thyrotropin receptor auto-antibody; Thyroid Stimulating auto-antibody

Test ID
General Information

Useful for:

  • Second-order testing for autoimmune thyroid disease, including:

  • Differential diagnosis of etiology of thyrotoxicosis in patients with ambiguous clinical signs or contraindicated (eg, pregnant or breast-feeding) or indeterminate thyroid radioisotope scans

  • Diagnosis of clinically suspected Graves disease (eg, extrathyroidal manifestations of Graves disease: endocrine exophthalmos, pretibial myxedema, thyroid acropachy) but normal thyroid function tests

  • Determining the risk of neonatal thyrotoxicosis in a fetus of a pregnant female with active or past Graves disease

  • Differential diagnosis of gestational thyrotoxicosis versus first-trimester manifestation or recurrence of Graves disease

  • Assessing the risk of Graves disease relapse after antithyroid drug treatment

  • A combination of TSI (Thyroid-Stimulating Immunoglobulin, Serum) and THYRO (Thyrotropin Receptor Antibody, Serum) is useful as an adjunct in the diagnosis of unusual cases of hypothyroidism (eg, Hashitoxicosis)

Specimen Type


Specimen Requirements

  • Preferred: Red Top

  • Acceptable: Serum Gel


  • Frozen (preferred): 60 days

  • Refrigerated: 7 days

  • Ambient: 24 hours

Unacceptable Specimen Conditions

Gross hemolysis


  • Positive results are strongly indicative of Graves disease, but do not always correlate with the presence and severity of hyperthyroidism

  • Patients with Hashimoto disease may have an elevated thyroid-stimulating immunoglobulins (TSI) index, which can be above 1.8. A TSI index of above 1.3 and less than or equal to 1.8 also is occasionally observed in various other thyroid disorders, including nodular goiter, and subacute thyroiditis


Recombinant Bioassay

Estimated TAT

2-6 days

Testing Schedule



3 months

CPT Code(s)


Additional Information
Minimum Sample Volume

0.1 mL

Reference Range

≤ 1.3 TSI index

Performing Lab


LOINC Code(s)