Thyroid Stimulating Immunoglobulin (Sendout)

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 and Thyrotropin Receptor Antibody [TSHR] is useful as an adjunct in the diagnosis of unusual cases of hypothyroidism (eg, Hashitoxicosis).

***Mayo Test Delay Update 04/15/2025: Turnaround time is expected to be 7 to 14 days for a minimum of four weeks.***

Cautions: 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.

3 mL blood in RED TOP tube or GOLD SST

Unacceptable: Any tube with anticoagulant

Outside Laboratories: Centrifuge sample and transfer serum to a separate plastic vial. Freeze serum at -20°C while awaiting shipment. Transport on dry ice.

Stability: Frozen (preferred): 60 days; Refrigerated: 7 days; Ambient: 24 hours.

Reject Due To: Gross hemolysis. Gross lipemia and gross icterus are acceptable.

Centrifuge sample and transfer serum to a separate plastic vial. Freeze at -20°C.

Sendouts:

• Order Mayo Test: TSI
• Interfaced: Yes [Interface: 601; Worksheet: MAFZ]

Stability: Frozen (preferred): 60 days; Refrigerated: 7 days; Ambient: 24 hours.

Reject Due To: Gross hemolysis. Gross lipemia and gross icterus are acceptable.