Autoantibody Tests

Autoantibody Tests

Summary

Autoantibody tests are blood tests that detect misguided antibodies. Normally, the immune system releases antibodies to fight foreign invaders (antigens), such as bacteria and viruses. In some people, however, antibodies mistakenly attack the body’s own tissues. These are known as autoantibodies.

Autoantibodies are found in many people with autoimmune diseases, including type 1 diabetes. Three autoantibodies are especially common in people with type 1 diabetes:

  • Insulin autoantibodies
  • Islet cell antibodies
  • Glutamic acid decarboxylase (GAD) autoantibodies

Researchers are developing autoantibody tests and genetic tests that can identify who is at risk of type 1 diabetes and that one day may even help prevent the disease.

Patients may also have autoantibody testing for other autoimmune endocrine diseases, such as Hashimoto’s thyroiditis and Graves’ disease, and for autoimmune musculoskeletal conditions including rheumatoid arthritis and lupus.

Autoantibody tests & diabetes

Autoantibody tests are blood tests that detect misguided antibodies. In healthy people, the immune system releases proteins known as antibodies, which attack foreign invaders (antigens) such as bacteria, viruses and cancer cells. Autoantibodies are antibodies that mistakenly destroy the body’s own tissues. Autoantibodies are found in many people with autoimmune diseases, including type 1 diabetes and latent autoimmune diabetes of adulthood.

The risk of developing type 1 diabetes is thought to be related to both genetics and environment. Research has shown the presence of certain autoantibodies or “markers” in an individual increases the risk for developing type 1 diabetes. Autoantibody testing is one of the best predictive methods for type 1 diabetes, but these tests are still conducted mainly in research settings.

In people with type 1 diabetes, the immune system’s antibodies mistakenly attack the insulin the body is producing, the islet cells of the pancreas that produce insulin, and glutamic acid decarboxylase (GAD), an enzyme found on the surface of beta cells. As a result, the body eventually fails to produce insulin.

Autoantibodies against islet cell antigens are important markers of type 1 diabetes, an autoimmune disease. These markers can be used to:

  • Identify people at risk for type 1 diabetes
  • Identify people who require insulin treatment
  • Aid in the classification of diabetes
  • Study the natural history of diabetes
  • Measure outcomes in intervention trials

Because the antibodies can be present several years before the diagnosis of type 1 diabetes, researchers have found their identification helpful in screening high-risk individuals. The presence of these antibodies means that the person has a greater chance of developing type 1 diabetes, not that the disease will definitely develop. According to the American Diabetes Association (ADA):

  • 70 to 80 percent of people newly diagnosed with type 1 diabetes have islet cell antibodies
  • 30 to 50 percent of people newly diagnosed with type 1 diabetes have antibodies to insulin
  • 80 to 95 percent of people newly diagnosed with type 1 diabetes have antibodies to GAD

In people with a parent or sibling with the disease, the risk of developing type 1 diabetes is only 1 to 10 percent. However, this risk greatly increases when autoantibodies are detected. For many people, the risk increases even more when combinations of autoantibodies and certain genes are present.

At this time, autoantibody tests are used primarily in diabetes research. The tests are usually conducted on individuals with a first- or second-degree relative with diabetes. One such study is being conducted by the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). The study, known as the Diabetes Antibody Standardization Study (DASP), is working to improve the measurement of autoantibodies for the prediction of type 1 diabetes.

Other projects include the Environmental Determinants of Diabetes in the Young (TEDDY). Its goal is to screen about 220,000 infants with genetic tests and follow at-risk individuals for 15 years.

The Search for Diabetes in Youth Study (SEARCH) uses autoantibody testing to distinguish between type 1 and type 2 diabetes. Its intent is to assist healthcare providers in classifying a patient’s form of diabetes.

In the Pacific Northwest, a region with an increased prevalence of type 1 diabetes, the Diabetes Evaluation in Washington study (DEW-IT) uses state birth records as an initial screening. The 17 percent of children identified as at-risk are offered additional blood tests starting around age 5. Of that group, about 10 percent test positive for diabetes autoantibodies.

Researchers are also trying to identify autoantibodies that may develop in healthy women during pregnancy and lead to type 1 diabetes in their children.

Scientists in Pittsburgh recently reported improving the ability to predict who is at risk of type 1 diabetes. By using older chemical tests identifying islet cell antibodies along with newer tests relying on biochemical markers to find islet autoantibodies, they found that:

  • Participants who had the two most frequently recognized autoantibodies had a 14 percent chance of developing type 1 diabetes after a decade.
  • Those who had the two autoantibodies as well as islet cell antibodies had an 80 percent risk after less than seven years.

Identification of those at high risk of type 1 diabetes shows who could benefit from a preventive vaccine when one is developed, according to the scientists.

The ADA recommends that only high-risk individuals undergo autoantibody testing and that those with positive results be referred to centers participating in prevention studies or other scientific investigations. Numerous trials are under way to try to prevent type 1 diabetes, including potential vaccines and treatments using immunosuppressive drugs.

It is hoped that in the future, autoantibody tests can be used with the general population to identify those at risk for type 1 diabetes. Early identification will provide the opportunity for earlier treatment. With earlier treatment, the individual has a greater chance of reducing the risk of medical conditions and complications. The test  would enable those at risk to watch for symptoms of the disease and be monitored by medical professionals. In addition, it is believed these tests can be used to distinguish between type 1 and type 2 diabetes.

Antibody tests have long been used for autoimmune disorders such as lupus and rheumatoid arthritis and for other conditions such as allergies, hepatitis and HIV (human immunodeficiency virus).

Other autoantibody tests

Though autoantibody testing for type 1 diabetes is still in its infancy, it has long been used for other autoimmune disorders such as lupus. In addition, antibody tests are used for immune system disorders such as allergies, hepatitis and HIV (human immunodeficiency virus).

Autoantibodies may be tested during the diagnosis, and sometimes during the monitoring, of many conditions. Examples include:

  • Thyroid autoantibodies. The most common thyroid antibodies include those to thyroglobulin and an enzyme called thyroid peroxidase (TPO). They most often indicate Hashimoto’s thyroiditis but can also suggest conditions including Graves’ disease and nontoxic goiter, according to the U.S. Food and Drug Administration (FDA). In addition, about half of the patients with Graves’ disease have antibodies to thyroid-stimulating immunoglobulin (TSI), according to the FDA.
  • Antinuclear antibody (ANA). ANA testing is often performed when an autoimmune musculoskeletal disease such as systemic lupus erythematosus or rheumatoid arthritis is suspected. However, an abnormally high amount of this common autoantibody can also be due to other conditions such as Hashimoto’s thyroiditis or Addison’s disease, or to certain medications such as TNF inhibitors.

Further diagnostic testing is needed, such as an analysis of synovial (joint) fluid or blood tests for rheumatoid factor or C reactive protein. Additional autoantibody testing can help, such as anti-double strand DNA (dsDNA) and anti-smith (Sm) for lupus and cyclic citrullinated peptide (CCP) for rheumatoid arthritis.

Researchers have developed saliva tests for diseases including HIV and an autoimmune disease called Sjogren’s syndrome. Autoantibody testing of saliva may one day become common.

Questions for your doctor

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about autoantibody tests:

  1. Do you recommend diabetes autoantibody tests for me?
  2. Will I also undergo genetic tests or other testing?
  3. When will my results be ready, and who will explain them to me?
  4. What are my test results?
  5. What does a positive antibody test show about my risk of developing type 1 diabetes?
  6. If my test shows I am at risk of diabetes, can I do anything to reduce this risk?
  7. If nothing can be done to prevent this disease, can I at least take steps to better prepare for it?
  8. How often should I have antibody testing or other monitoring?
  9. How can I participate in a clinical study of diabetes autoantibody testing?
  10. Should my children or other family members have autoantibody testing?
  11. If thyroid autoantibody testing is recommended for me, what can it show? What do my results mean?
  12. If autoantibody testing is recommended for me for other autoimmune diseases such as rheumatoid arthritis or lupus, what can it show? Are these results definitive, or would I need more testing?
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