IMMULITE 2000 and 2000 XPi TSI Assay

Graves’ disease (GD) is an autoimmune disorder caused by the presence of thyroid stimulating immunoglobulins (TSI) that bind to the TSH receptor on the thyroid cells and stimulate the uncontrolled production of thyroid hormones. Detecting the presence of TSI in the blood is a powerful diagnostic tool for the differential diagnosis of GD.

TSI measurements are also used to monitor the response to GD therapy and prediction of remission or relapse, confirm Graves’ ophthalmopathy, and predict neonatal thyroid hyperthyroidism.1,2

The IMMULITE® 2000 and 2000 XPi TSI assay is the first automated, quantitative TSI assay available. TSH receptor antibody (TRAb) assays detect both thyroid-blocking and -stimulating antibodies. However, blocking antibodies inhibit TSH stimulation of thyroid cells and lead to hypothyroidism. The IMMULITE 2000 and 2000 XPi TSI assay detects thyroid stimulating antibodies, the specific cause of GD pathology, with a clinical sensitivity and specificity of 98.3% and 99.7% respectively. With a 65-minute total assay time and ready-to-use, stable reagents, the use of this assay can make the differential diagnosis of GD faster and easier, allowing patients to be diagnosed and treated sooner.

Understanding Graves' Disease

Graves’ disease is an autoimmune disorder that leads to overactivity of the thyroid gland—hyperthyroidism. It is caused by an abnormal immune system response that causes the thyroid gland to produce too much thyroid hormone. The thyroid gland is a butterfly-shaped organ that lies flat against the windpipe in the throat. It produces the hormones thyroxine (T4) and triiodothyronine (T3) and plays an important role in controlling the body's metabolism.3

What are the symptoms of Graves’ disease?4
People with Graves’ disease may have common symptoms of hyperthyroidism, such as:

  • Nervousness or irritability
  • Fatigue or muscle weakness
  • Heat intolerance
  • Trouble sleeping
  • Hand tremors
  • Rapid and irregular heartbeat
  • Frequent bowel movements or diarrhea
  • Weight loss
  • Goiter, which is an enlarged thyroid that may cause the neck to look swollen and can interfere with normal breathing and swallowing

In addition, the eyes of people with Graves’ disease may appear enlarged because their eyelids are retracted—seemingly pulled back into the eye sockets—and their eyes bulge out from the eye sockets. This condition is called Graves’ ophthalmopathy.4

Who is likely to develop Graves’ disease?
Graves’ disease usually occurs in people younger than age 30 and is more common in women than men.4

Factors such as age, sex, heredity, and emotional and environmental stress are likely involved in Graves’ disease. And a person’s chance of developing Graves’ disease increases if other family members have the disease or Hashimoto's disease. The disorders probably develop from a combination of genes and an outside trigger, such as a virus.4

Laboratory testing
Laboratory testing is essential to verify the diagnosis, estimate disease severity, and monitor and assist in planning therapy for Graves’ disease patients. To detect thyroid dysfunction, testing may begin with:

  • TSH: typically low in Graves’ disease
  • Total T4 or free T4: usually elevated
  • Total T3 or free T3: often elevated

The above tests may also be ordered periodically to monitor thyroid function and hormone production.

Laboratory tests used to help diagnose Graves’ disease and distinguish it from other autoimmune conditions may include one or more tests used to detect the presence of thyroid antibodies:3

  • Thyroid stimulating immunoglobulin (TSI): The presence of this antibody is diagnostic for Graves’ disease.
  • Thyroid stimulating hormone receptor antibody (TRAb): Less specific than TSI.
  • Anti-thyroid peroxidase antibody (anti-TPO): This autoantibody is found in most people with Graves’ disease, as well as in Hashimoto thyroiditis.

Assay Specifications

Sample Type

Serum, plasma (Li heparin, EDTA)

Sample Volume
50 µL
Assay Range

0.10–40 IU/L

Limit of Quantitation
0.10 IU/L
Calibration Interval
4 weeks
Onboard Stability
90 days
Time to First Result
65 minutes
Clinical Sensitivity
Clinical Specificity

Educational Resources

Educational Video: Diagnosing Graves’ Disease

Watch this 7-minute educational video on the important role of TSI in the diagnosis of Graves’ disease.

women and thyroid disease

Explore the clinical and pathophysiological aspects of Graves' disease and the clinical application of the TSI assay.

TSI literature compendium

TSI literature compendium

Third-party articles comparing the diagnostic value of the IMMULITE 2000 TSI assay (a bridge assay) to TRAb assays.