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Test Name:
Glutamic Acid Decarboxylase Antibody
- SBMF No:
28276 - Performance Lab Name:
Immunology - Test Mnemonic:
GAD - ABN:
Not required - CPT Code:
83520 - LOINC Code:
13926-1 - Also Known As:
GAD Antibody
GAD65 Antibody
Stiff-Person Syndrome (SPS) - Spec Type:
Serum - Spec Container:
Gold top (SST) or red top (serum) tube - Pref Vol:
0.25 mL - Min Vol:
0.1 mL - Fasting:
No - Spec Collect:
Routine venipuncture - Spec Process:
Clot 30 minutes
Promptly centrifuge 15 minutes
Immediately transfer serum to separate plastic tube and freeze - Spec Store Transport:
Frozen (preferred)
Refrigerated OK - Spec Stability:
After separation from cells:
2 hours room temperature (20-30°C)
1 week refrigerated (2-8°C)
1 week frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Spec Reject:
Sample at room temperature longer than 2 hours
Severely hemolyzed or lipemic sample - Spec Remarks:
Separate serum from cells ASAP or within 2 hours of collection - Methodology:
Enzyme-Linked Immunosorbent Assay (ELISA) - Use:
Detect the presence of antibodies to glutamic acid decarboxylase (GAD65), which provides early evidence of autoimmune disease activity. Its measurement has been shown to be useful in assisting physicians in the prediction, diagnosis, and management of patients with diabetes. - Clinical Significance:
Glutamic acid decarboxylase (GAD) is the enzyme responsible for the synthesis of neurotransmitter gamma-aminobutyric acid in neurons and pancreatic beta cells. It is represented by two isoforms, GAD65 and GAD67, which are the products of two different genes. GAD65 is the dominant autoantigen in stiff-person syndrome (SPS) and insulin-dependent diabetes mellitus (IDDM).
In SPS, the immune system makes antibodies against GAD65. GAD65 plays an important role in the production of gamma-aminobutyric acid (GABA), a neurotransmitter that inhibits certain activity in the spinal cord and brain.
Type I diabetes, IDDM, accounts for approximately 15% of the diabetic population. IDDM is generally seen in children and young adults, but it can strike at any age. Insulin deficiency results in autoimmune destruction of insulin producing pancreatic beta cells. Clinical onset of diabetes does not occur until 80-90% of these cells are destroyed. Prior to clinical onset, type1 diabetes can be characterized by lymphocytic infiltration of the islet cells and various circulating autoantibodies. Measuring these autoantibodies as disease markers at the pre-diabetic stage affords an opportunity to predict and prevent the clinical onset of the disease.
GAD65 antibodies have been found in 70-90% of pre-diabetic and Type 1 diabetic patients. It is the most sensitive single marker for identifying individuals at risk of developing diabetes. GAD65 is more prevalent in older children and late-onset Type 1 diabetes and the marker has been shown to be detected ten years prior to disease onset.
- Reference Range:
Less than 5 U/mL - Day Run:
Thu - Time Run:
8:00 am - Time Reported:
5:00 pm - Test Type:
IMMUNOLOGY
