GAD65 Ab Assay (Sendout)

Useful For:

• Assessing susceptibility to autoimmune (type 1, insulin-dependent) diabetes mellitus and related endocrine disorders (eg, thyroiditis and pernicious anemia)
• Distinguishing between patients with type 1 and type 2 diabetes
• Confirming a diagnosis of stiff-man syndrome, autoimmune encephalitis, autoimmune ataxia, brain stem encephalitis, autoimmune epilepsy, autoimmune myelopathy

Ordering Guidance: GAD65 Antibody is the recommended first-line test for suspected Stiff-Person Syndrome. If the GAD65 Antibody result is negative, Stiff-Person Spectrum Disorders Evaluation, Serum (Sendout) may be considered for follow-up testing. If the panel is desired, submit an Epic LADDON (Laboratory Add On) request for OLTG #1108/Mayo Test SPPS and specify that testing should be added to the sample at Mayo Clinic Laboratories. Specimens are stored at Mayo for up to 28 days.

Reference values apply to all ages.

Interpretation:

High titers (> or =20.0 nmol/L) are found in classic stiff-person syndrome (93% positive) and in related autoimmune neurologic disorders (eg, acquired cerebellar ataxia, some acquired non-paraneoplastic encephalomyelopathies).

Diabetic patients with polyendocrine disorders generally have glutamic acid decarboxylase antibody values 0.02 nmol/L or above.

Values in patients who have type 1 diabetes without a polyendocrine or autoimmune neurologic syndrome are usually 0.02 nmol/L or below. Low titers (0.03-19.9 nmol/L) are detectable in the serum of approximately 80% of type 1 diabetic patients. Conversely, low titers are detectable in the serum of less than 5% of patients with type 2 diabetes. Testing for autoimmune type 1 diabetes is complimented by testing for insulin, islet cell (IA-2), and ZnT8 antibodies.

Eight percent of healthy Olmsted County residents over age 50 years have low-positive values and may be at risk for future autoimmune disease.

Values 0.03 nmol/L or above are consistent with susceptibility to autoimmune (type 1) diabetes and related endocrine disorders (thyroiditis and pernicious anemia).

Outside Laboratories: Centrifuge sample and transfer serum to a separate plastic vial. Refrigerate serum while awaiting shipment. Ship sample with a cold pack.

Stability: Refrigerated (preferred): 28 days; Frozen: 28 days; Ambient: 72 hours.

Reject Due To: Gross hemolysis, lipemia, or icterus.

Centrifuge sample and transfer serum to two separate plastic vials. If sample volume is low, prioritize the sendout test (RGAD65).

• RGAD65: Refrigerate serum (Sendouts Mayo Rack).
• UW417: Freeze sample at -20°C in Immunology rack.

Sendouts:

• Order Mayo Test: GD65S
• Interfaced: Yes [Interface: 601; Department: MARF]

Stability: Refrigerated (preferred): 28 days; Frozen: 28 days; Ambient: 72 hours.

Reject Due To: Gross hemolysis, lipemia, or icterus.