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Many people, and even many doctors, have not heard of antibody tests, which can aid in the diagnosis of type 1 diabetes. The blood tests measure your body’s specific antibodies related to autoimmune activity that attacks insulin-producing beta cells in the pancreas, says Lori Laffel, MD, chief of the section on Pediatric, Adolescent, and Young Adult Diabetes at Joslin Diabetes Center and professor of pediatrics at Harvard Medical School.
You do not need to prepare for antibody tests. There are five antibody tests; they each measure different antibodies. For the C-peptide test, fasting is required. More than one test may be done because any given single test may be negative for type 1.
- C-Peptide—Instead of checking for antibodies, this test measures how much C-peptide is in your blood. Because levels of this peptide generally match insulin levels in the body, the test can indicate how much insulin your body is producing. Low levels of C-peptide and insulin usually point to type 1 diabetes.
- Glutamic Acid Decarboxylase Autoantibodies (GADA or Anti-GAD)—This test looks for antibodies built against a specific enzyme in the pancreatic beta cells that produce insulin.
- Insulin Autoantibodies (IAA)—In addition to attacking beta cells, the immune system in people with type 1 diabetes also targets insulin, says Laffel. This tests looks for the antibodies targeting insulin.
- Insulinoma-Associated-2 Autoantibodies (IA-2A)—This test looks for antibodies mounted against a specific enzyme in beta cells. Both the IA-2A and GADA tests are common type 1 antibody tests performed at endocrinology offices.
- Islet Cell Cytoplasmic Autoantibodies (ICA)—Islet cells are clusters of cells in the pancreas that sense blood glucose levels and dole out insulin accordingly. This test looks at the reaction between islet cell antibodies from humans and a variety of islet cell proteins (including beta cells) from an animal pancreas, says Laffel. If your antibodies react with the animal islet cells, you have a marker for type 1. This is the oldest type 1 antibody test, and is not used as frequently today.
- Zinc Transporter 8 (ZnT8Ab)—The newest type 1 test, this looks at antibodies targeting an enzyme that is specific to beta cells. This test may not be as readily available.