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Test Code TSI Thyroid-Stimulating Immunoglobulin, Serum

Test Down Notes

This test is temporarily unavailable. For additional details, see test update here.

Reporting Name

Thyroid-Stimulating Immunoglob, S

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).

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum


Ordering Guidance


This test is used for second-order testing for autoimmune thyroid disease.

 

For suspected cases of autoimmune hypothyroidism, the first-order testing is TPO / Thyroperoxidase Antibodies, Serum.

 

For suspected cases of autoimmune thyroid disease, first-order testing includes TPO and THYRO / Thyrotropin Receptor Antibody, Serum.



Specimen Required


Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.


Specimen Minimum Volume

0.3 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Frozen (preferred) 60 days
  Refrigerated  7 days
  Ambient  24 hours

Reference Values

≤1.3 TSI index

Reference values apply to all ages.

Day(s) Performed

Monday through Friday

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

84445

LOINC Code Information

Test ID Test Order Name Order LOINC Value
TSI Thyroid-Stimulating Immunoglob, S 30567-2

 

Result ID Test Result Name Result LOINC Value
8634 Thyroid-Stimulating Immunoglob, S 30567-2

Method Description

This bioassay compares the cyclic adenosine monophosphate (cAMP) production of thyrotropin (TSH)-responsive cells upon exposure to patient serum with that obtained in the same cells after exposure to normal control serum.

 

The assay uses Chinese hamster ovary cells that have been permanently transfected with the human TSH receptor (TSHR) and a luciferase expression construct under the control of a cAMP responsive promoter. Luciferase transcription in these cells is proportional to the concentration of intracellular cAMP.

 

The cells are grown to near confluence. An aliquot of cells is then incubated with each diluted patient serum. Cells are lysed at the end of incubation, luciferase substrate is added, and chemiluminescence is measured in a luminometer. The ratio of the light-units produced in the cell-lysate exposed to patient serum divided by a control cell-lysate light-signal is the TSI index.(Preissner CM, Wolhuter PJ, Sistrunk JW, Homburger HA, Morris JC III. Comparison of thyrotropin-receptor antibodies measured by four commercially available methods with a bioassay that uses Fisher-rat thyroid cells. Clin Chem. 2003;49(8):1402-1404; package insert: Thyroid Stimulating Immunoglobulin Assay. Diagnostic Hybrids; PI4035011EN00, 10/2020)

Report Available

2 to 6 days

Reject Due To

Gross hemolysis Reject
Gross lipemia OK
Gross icterus OK

Method Name

Recombinant Bioassay

Forms

If not ordering electronically, complete, print, and send a General Request (T239) with the specimen.

Secondary ID

8634