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Thyroid Stimulating Immunoglobulin (TSI), Serum — Concentration

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

A blood test that measures thyroid-stimulating antibodies, most often used to help evaluate Graves disease and other autoimmune thyroid conditions.

Quick summary

["An elevated TSI level can support a diagnosis of Graves disease when combined with the results of other thyroid tests."]

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

Key facts at a glance

LOINC
30567-2
Short code
TSI Ser-aCnc
Synonyms
TSI Ser-aCnc
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?

The thyroid-stimulating immunoglobulin (TSI) test measures the level of antibodies in blood that can stimulate the thyroid gland. These antibodies target the thyroid-stimulating hormone receptor and can cause the thyroid to produce too much hormone.

Why might I need this test?

This test may be ordered when symptoms or other thyroid tests suggest an overactive thyroid. It is especially useful when Graves disease, including thyroid eye disease, is suspected. Your clinician will interpret it alongside your medical history and other laboratory results.

How is the test performed?

A blood sample is collected and tested in a laboratory to determine the amount of thyroid-stimulating immunoglobulin present. No radioactive tracer or special imaging is required.

How do I prepare for the test?

You generally do not need special preparation for this blood test. Tell your clinician about any thyroid medicines or other treatments you are taking, and do not stop prescribed medication unless instructed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

TSI test

Frequently asked questions

What does a high TSI level mean?
A high level means you have antibodies that stimulate the thyroid receptor, which is commonly associated with Graves disease. The result is interpreted together with thyroid hormone tests and your symptoms.
Is the TSI test the same as a TSH test?
No. The TSI test measures stimulating antibodies, while the TSH test measures the amount of thyroid-stimulating hormone released by the pituitary gland.
Does a negative TSI result rule out Graves disease?
Not always. Some people with Graves disease may have a negative TSI result, so your clinician may consider other thyroid antibody tests and clinical findings.
  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