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Thyroid Stimulating Immunoglobulin

Test Codes

TSI, Thyroid Stimulating Antibody, TSH Receptor Antibody, EPIC: LAB7104, SOFT: TSHIG

Specimen Collection Criteria

Collect: One Gold-top SST tube. (Minimum Whole Blood: 2.0 mL)

Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged collection tube within eight hours of collection. (Minimum Serum: 0.5 mL)

Preparation for Courier Transport

Transport: Centrifuged collection tube, refrigerated (2-8°C or 36-46°F). (Minimum Serum: 0.5 mL)

Rejection Criteria

• Plasma specimens. 
• Severely lipemic, icteric, or grossly hemolyzed specimens.    

In-Lab Processing

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Room temperature is acceptable for a maximum of eight hours. (Minimum Serum: 0.5 mL)

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 8 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gels
Room Temperature (20-26°C or 68-78.8°F): 2 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 8 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 6 months

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Royal Oak Special Testing Laboratory

Performed

Monday – Friday.
Results available within 2 business days

Reference Range

Negative: <0.10 IU/L
Positive: >0.10 IU/L

A test cut-off of 0.55 IU/L improves the clinical sensitivity and specificity for Graves disease to 98.6% and 98.5%, respectively.  Although not common, low TSI values may be observed in patients with non-Graves thyroid disorders, or other autoimmune diseases. 

Test Methodology

Chemiluminescent Immunoassay

Clinical Utility

The TSH receptor (TSHR) harbors a large extracellular domain.  Patients with Graves disease commonly develop autoantibodies to epitopes present on the extracellular domain of the TSH receptor.  Such autoantibodies can be stimulatory or inhibitory in nature.  Those that are stimulatory (i.e. TSI), mimic TSH stimulation.  In contrast to TSH, thyroid stimulating immunoglobulins are not subject to a negative feedback mechanism, and thus potentiate autoimmune thyroid disease pathogenesis.  

TSI should be used as a second-order test in autoimmune thyroid disease, including:

1. To aid in the diagnosis of thyrotoxicosis if patient has ambiguous clinical presentation or thyroid scan is indeterminate/cannot be performed.
2. To support the diagnosis of clinically suspected Graves disease in patients with normal thyroid function tests. 
3. As a prognostic marker for relapse of Graves disease.
4. To predict the risk of thyroid dysfunction in a fetus of a pregnant female with active or treated Graves disease.

Reference

Renato Tozzoli et al., Clinical Chemistry Laboratory Medicine, Volume 55, pages 58-64, 2017.   

CPT Codes

84445
LOINC: 30567-2

Contacts

Last Updated

1/13/2023