GAD65 Ab Assay (Sendout)

General Information

Lab Name

GAD65 Ab Assay

Lab Code

RGD65

Epic Name

GAD65 Antibody Assay (Sendout)

External Test Id

GD65S

Description

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.

References

Mayo Clinical & Intepretive Information: Glutamic Acid Decarboxylase (GAD65) Antibody Assay, Serum

Synonyms

64K Antibody, Anti GAD Ab, Anti-Glutamic Acid Decarboxylase Ab, Ataxia, Beta Cell Antibody, GD65S, Islet Cell Antibody, Pancreatic Islet Cell Ab, Stiff person, Stiff-man syndrome, Stiffman Syndrome

Components

Code	Name
RGAD65	GAD65 Antibody Assay
UW417	Imm Study_GAD65 Antibody

Interpretation

Method

Radioimmunoassay (RIA)

Reference Range

See individual components

Ref. Range Notes

Reference Range:

< or =0.02 nmol/L

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).

Interferences and Limitations

Cautions: Antibodies specific for glutamic acid decarboxylase (GAD65) account for most, but not all, antibodies detected in the islet cell antibody test (IA-2). IA-2 (a protein tyrosine kinase-like protein), insulin, and zinc transporter-8 antibodies are complementary islet cell antibodies.

References

Mayo Clinical & Intepretive Information: Glutamic Acid Decarboxylase (GAD65) Antibody Assay, Serum

Ordering & Collection

Specimen Type: Blood
Collection: 6 mL blood in a RED top tube or GOLD SST
Handling Instructions: 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.
Quantity: Requested: 1mL serum + 1mL serum for UW417
Minimum: 1 mL serum

Processing

Receiving Instructions

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.

Misc Sendout

Performance

Lab Department

Frequency

Performed: Monday through Sunday. Report Available: 3-6 days from sample receipt at Mayo Clinic Labs.

Available STAT?

Performing Location(s)

Sendout	Mayo Clinic Laboratories 800-533-1710 200 First Street Southwest Rochester, MN 55901

Billing & Coding

CPT Codes: 86341
LOINC: 30347-9
Interfaced Order Code: UOW3337