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Test Code LAB0231951 Glutamic Acid Decarboxylase (GAD65) Antibody Assay, Serum

Additional Codes

Mayo Test ID
GD65S

Performing Laboratory

Mayo Clinic Laboratories in Rochester

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

Method Name

Radioimmunoassay (RIA)

Reporting Name

GAD65 Ab Assay, S

Specimen Type

Serum


Ordering Guidance


This test should not be requested in patients who have recently received radioisotopes, therapeutically or diagnostically, because of potential assay interference. The specific waiting period before specimen collection will depend on the isotope administered, the dose given, and the clearance rate in the individual patient. Specimens will be screened for radioactivity prior to analysis. Radioactive specimens received in the laboratory will be held 1 week and assayed if sufficiently decayed or canceled if radioactivity remains.



Specimen Required


Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 1.5 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 28 days
  Frozen  28 days
  Ambient  72 hours

Reject Due To

Gross hemolysis Reject
Gross lipemia Reject
Gross icterus Reject

Reference Values

≤0.02 nmol/L

Reference values apply to all ages.

Interpretation

High titers (≥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).

Day(s) Performed

Monday through Sunday

Report Available

3 to 6 days

Specimen Retention Time

28 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

86341

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GD65S GAD65 Ab Assay, S 30347-9

 

Result ID Test Result Name Result LOINC Value
81596 GAD65 Ab Assay, S 30347-9