GAD antibodies or Glutamic Acid Decarboxylase (GAD65) Test: Purpose, Normal Range and Findings

Glutamic Acid Decarboxylase Antibodies test is used to determine whether the patient has Type 1 diabetes, Type 2 diabetes or Latent Autoimmune diabetes of adulthood.

Updated: October 28, 2019


Glutamic Acid Decarboxylase Antibodies test is used to determine whether the patient has Type 1 diabetes, Type 2 diabetes or Latent Autoimmune diabetes of adulthood. Glutamic acid decarboxylase (GAD) is an enzyme required for the pancreas to function normally. Antibodies that target this enzyme are called GAD antibodies. An antibody is a protein that your immune system uses to attack foreign objects, which are often potentially harmful, such as viruses or bacteria.
Sometimes, the immune system makes antibodies that mistakenly attack normal cells that aren't  harmful causing autoimmune disorder. GAD antibodies are found in the blood of most of the people with type 1 diabetes.This test is particularly done for the patients above the age of 30 who suffer from diabetes.

Purpose of GAD65 Test:

GAD antibody testing is primarily used to differentiate between type 1 diabetes from diabetes due to some causes. The test is done when a person is newly diagnosed with diabetes to know the type of diabetes in the body. Type 1 diabetes is due to lack of insulin where as type 2 diabetes develops due to insulin resistance. When a person is diagnosed as Type 2 but have a great difficulty in controlling his/her glucose levels with standard treatments, this test will be helpful.
Instead of a specific GAD test, you can also have an antibody panel test which include GAD and other antibodies. Other antibodies associated with type 1 diabetes include:

  • islet cell cytoplasmic autoantibodies (ICAs)
  • insulinoma-associated-2 autoantibodies (IA-2As)
  • insulin autoantibodies (IAAs), which are more common in children than adults

This test also determines whether gestational diabetes is type 1 diabetes or not. Along with type 1 diabetes mellitus detection, this test is also helpful in finding related endocrine disorders such as thyroiditis and pernicious anemia.
All of these tests are done by a simple blood test. You won't need to fast or do anything else to prepare. A healthcare professional will take blood from a vein in your arm and send it to a laboratory for analysis. The results usually arrive after 2-3 days. After taking the sample the area from where blood was taken out is bandaged by the health professional.You most likely have type 1 diabetes if GAD or any of these other antibodies are found. If no GAD antibodies are found, you probably have type 2.

Normal Range and Findings:

The normal value for GAD antibodies testing is less then or equal to 0.02 nmol/L. Greater then 0.02 nmol/L are found in classic stiff-man syndrome and in related autoimmune neurologic disorders such as acquired cerebellar ataxia, some acquired nonparaneoplastic encephalomyelopathies.
Diabetic patients with polyendocrine disorders also generally have glutamic acid decarboxylase (GAD65) antibody values greater then 0.02 nmol/L. patients who have type 1 diabetes without a polyendocrine or autoimmune neurologic syndrome will have usually less then 0.02 nmol/L.
Low titers which is between 0.03 to 19.9 nmol/L are detectable in the serum of most of type 1 diabetic patients. Patients with myasthenia gravis, Lambert-Eaton syndrome, and rarer autoimmune neurological disorders will also have low titers.

Causes of high GAD antibody levels:

Type 1 diabetes is not the only reason someone might have high GAD antibodies. They are also linked to other conditions, which include:

  • stiff person syndrome, which is a neurological condition that causes stiff muscles and muscle spasms
  • cerebellar ataxia, which is a brain disorder that causes sudden, uncoordinated muscle movement
  • other autoimmune diseases, including rheumatoid arthritis and thyroid disease

If you are diagnosed with diabetes and GAD antibodies are found in the serum, it is likely that you have type 1 diabetes.


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