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Thyroid-Stimulating Immunoglobulin, Serum

Published: August 9, 2026Updated: August 16, 2026

A blood test that detects thyroid-stimulating antibodies, most often used to help evaluate Graves disease and other causes of hyperthyroidism.

Quick summary

["A positive TSI result can support a diagnosis of Graves disease when combined with other thyroid test results."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
110118-7
Short code
TSI Msmt Ser
Synonyms
TSI Msmt Ser
Category
thyroid
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What is this test?

Thyroid-stimulating immunoglobulin (TSI) is a type of antibody that can attach to thyroid hormone receptors and stimulate the thyroid gland. This test measures TSI in a blood sample.

Why might I need this test?

TSI testing may be ordered when symptoms or other laboratory results suggest an overactive thyroid. It is especially useful for confirming Graves disease, an autoimmune cause of hyperthyroidism.

How is the test performed?

A blood sample is collected from a vein and sent to a laboratory. The laboratory uses a specialized assay to detect and measure thyroid-stimulating antibodies.

How do I prepare for the test?

Fasting is usually not required, but follow any instructions provided by your healthcare professional. Tell the laboratory if you take thyroid medicines, iodine or iodine-containing supplements, or biotin supplements, because these may affect interpretation.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

TSI

Frequently asked questions

Is TSI the same as a thyroid-stimulating hormone test?
No. TSH is a hormone made by the pituitary gland that tells the thyroid how much hormone to produce, while TSI is an antibody that can directly stimulate thyroid hormone receptors.
What symptoms can lead to TSI testing?
Testing may be considered with an irregular or rapid heartbeat, tremor, heat intolerance, weight loss despite increased appetite, anxiety, frequent bowel movements, or an enlarged thyroid.
Does a positive TSI result mean I have Graves disease?
A positive result supports Graves disease, especially when thyroid function tests also show hyperthyroidism. The result should be interpreted by a healthcare professional because other clinical findings are needed for a definitive diagnosis.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy