IMMULITE 2000/2000 XPi TSI Assay

IMMULITE 2000/2000 XPi TSI Assay
 
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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, confirming Graves’ ophthalmopathy, and for predicting neonatal thyroid hyperthyroidism.1,2 Incorporating the TSI assay into existing diagnostic algorithms has been shown to reduce overall direct costs of GD diagnosis by up to 43%, with the net cost of avoiding misdiagnosis reduced by up to 85%.3

The IMMULITE® 2000/2000 XPi TSI assay is the first automated and quantitative TSI assay available today. 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 2000/2000 XPi TSI assay detects thyroid stimulating antibodies, the specific cause of GD pathology, with a clinical sensitivity and specificity of 98.6% and 98.5% 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.
 

Assay Specifications

IMMULITE 2000 TSI Assay

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 Interval4 weeks
Onboard Stability
90 days
Time to First Result
65 minutes
Clinical Sensitivity

98.3%

Clinical Specificity

99.7%

Traceable to the WHO 2nd International Standard NIBSC 08/204

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.4

What are the symptoms of Graves’ disease?5
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—seem pulled back into the eye sockets—and their eyes bulge out from the eye sockets. This condition is called Graves’ ophthalmopathy.5

Who is likely to develop Graves’ disease?

Graves’ disease usually occurs in people younger than age 40 and is seven to eight times more common in women than men.5 Women are most often affected between ages 30 and 60.5
According to the National Women's Health Information Center, Graves’ disease affects about 2% of women at some time in their lives.
 

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. Researchers have not been able to find a specific gene that causes the disease to be passed from parent to child. While scientists know some people inherit an immune system that can make antibodies against healthy cells, predicting who will be affected is difficult. 5

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

  • TSH — typically low in Graves’ disease
  • Total or free T4 — usually elevated
  • Total 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:4

  • 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.
     

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1Gupta, Manjula K. Thyrotropin-receptor antibodies in thyroid diseases: advances in detection techniques and clinical applications. Clinica Chimica Acta. 2000;293:1-29

2M.R. Bjorgaas, H. Farstad, S.C. Christiansen, H-G.K. Blaas. Impact of thyrotrophin receptor antibody levels on fetal development in two successive pregnancies in a woman with Graves’ disease. Horm, res. Paediatr. 79:39-43, 2012.

3McKee A., Peyerl, F. TSI assay utilization: impact on costs of Graves’ hyperthyroidism diagnosis. AJMC. 2012; 18(1):1-15.

4http://labtestsonline.org/understanding/conditions/graves/

5http://www.endocrine.niddk.nih.gov/pubs/graves/

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