GAD65 Antibody (Sendout)

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General Information

Lab Name
GAD65 Antibody Assay
Lab Code
RGAD65
Epic Ordering
GAD65 Antibody (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 Note: Non-orderable sendout battery included in the GAD65 Ab Assay (Sendout) [RGD65] package.

References
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

Interpretation

Method

Radioimmunoassay (RIA)

Reference Range
Units: nmol/L
Female Male
AgeRangeAgeRange
0-0-0.02 0-0-0.02

Effective date: 06/01/2023

Ref. Range Notes

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

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

Processing

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.

Performance

LIS Dept Code
Sendouts Mayo Lab (RF) (MARF)
Performing Location(s)
Sendout Mayo Clinic Laboratories
800-533-1710

200 First Street Southwest
Rochester, MN 55901
Frequency
Available STAT?
No

Billing & Coding

CPT codes
86341
Billing Comments

Radioimmunoassay (RIA)

LOINC
30347-9
Interfaced Order Code
UOW1802
Interfaced Result Code
UOW1802