Thyroid Stimulating Immunoglobulin (Sendout)

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General Information

Lab Name
Thyroid Stim. Immunoglobulin
Lab Code
RTSI
Epic Name
Thyroid Stim Immunoglobulin
External Test Id
TSI
Description

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.***

    References
    Synonyms
    FFTSI, LATS (Long Acting Thyroid Stimulator), Long Acting Thyroid Stimulators, Long-Acting Thyroid Stimulator, TSI
    Components

    Interpretation

    Method

    Recombinant Bioassay

    Reference Range
    Units: TSI Index
    Female Male
    AgeRange AgeRange
    0-<1.4 0-<1.4

    Effective date: 03/22/2006

    Interferences and Limitations

    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.

    References

    Ordering & Collection

    Specimen Type
    Blood
    Collection

    3 mL blood in RED TOP tube or GOLD SST

    Unacceptable: Any tube with anticoagulant

    Handling Instructions

    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.

    Quantity
    Requested: 3 mL serum
    Minimum: 0.5 mL serum

    Processing

    Receiving Instructions

    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.

    Misc Sendout

    Performance

    Lab Department
    Sendouts Mayo Lab (FZ)(MAFZ)
    Frequency
    Performed: Monday through Friday. Report Available: 2-6 days from sample receipt at Mayo Clinic Labs.
    Available STAT?
    No
    Performing Location(s)
    Sendout Mayo Clinic Laboratories (Superior Drive)
    800-533-1710

    3050 Superior Drive NW
    Rochester, MN 55901

    Billing & Coding

    CPT Codes
    84445
    LOINC
    30567-2
    Interfaced Order Code
    UOW1913
    Interfaced Result Code
    UOW1913