GAD-65 Antibody Test (Glutamic Acid Decarboxylase Antibody Test)

What is the GAD-65 Test?

The GAD-65 (Glutamic Acid Decarboxylase-65) antibody test is a blood test that detects autoantibodies against the GAD-65 enzyme. This test helps diagnose autoimmune conditions, primarily:

✅ Type 1 Diabetes (T1D) – GAD-65 antibodies target insulin-producing beta cells in the pancreas.
✅ Stiff-Person Syndrome (SPS) – A rare neurological disorder causing muscle stiffness and spasms.
✅ Other Autoimmune Diseases – Sometimes associated with thyroid disorders, ataxia, epilepsy, or polyendocrine syndromes.

Why is the Test Done?

📌 To differentiate Type 1 diabetes (autoimmune) from Type 2 diabetes.
📌 To diagnose Stiff-Person Syndrome (SPS) or other neurological disorders.
📌 To assess the risk of autoimmune diabetes in family members.

Test Procedure

• Sample Type: Blood sample (serum)
• Fasting Required: No
• Test Method: ELISA (enzyme-linked immunosorbent assay) or Radioimmunoassay (RIA)

Interpreting the Results

• Strongly Positive in Type 1 Diabetes: Suggests an autoimmune cause of diabetes.
• Strongly Positive in Stiff-Person Syndrome: Indicates neurological autoimmune disease.
• May be seen in other conditions: Autoimmune thyroid disorders, cerebellar ataxia, or epilepsy.

Follow-Up After a Positive Test

✅ C-Peptide Test – Helps assess insulin production (low in Type 1 diabetes).
✅ Other Autoantibody Tests – ICA (Islet Cell Antibodies), IA-2, or ZnT8 antibodies for diabetes.
✅ Neurological Tests – If Stiff-Person Syndrome is suspected.

Key Points

✔ GAD-65 antibodies are NOT seen in Type 2 diabetes.
✔ High levels indicate autoimmune destruction of pancreatic cells.
✔ May help predict Type 1 diabetes in at-risk individuals.