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Test ID: GD65C Glutamic Acid Decarboxylase (GAD65) Antibody Assay, Spinal Fluid

Reporting Name

GAD65 Ab Assay, CSF

Useful For

Possible use in evaluating patients with stiff-man syndrome, autoimmune cerebellitis and other acquired central nervous system disorders affecting gabaminergic neurotransmission

Clinical Information

Glutamic acid decarboxylase (GAD) is a neuronal enzyme involved in the synthesis of the neurotransmitter gamma-aminobutyric acid (GABA). Serum antibodies directed against the 65-kd isoform of GAD (GAD65) are detected in heightened frequency in a variety of autoimmune neurologic disorders, including stiff-man (Moersch-Woltman) syndrome, autoimmune cerebellitis, some idiopathically acquired epilepsies, some rare acquired encephalomyelopathies with and without neoplasia, and in myasthenia gravis and Lambert-Eaton myasthenic syndrome.


GAD65 antibodies account for the majority of clinically recognized pancreatic islet cell antibodies, and are an important serological marker of predisposition to type 1 (insulin-dependent) diabetes. GAD65 autoantibodies also serve as a marker of predisposition to autoimmune disorders that commonly or sometimes coexist with type 1 diabetes, including autoimmune thyroid disease (eg, thyrotoxicosis, Graves disease, Hashimoto thyroiditis, hypothyroidism), pernicious anemia, premature ovarian failure, Addison disease (idiopathic adrenocortical failure), and vitiligo. GAD65 antibodies are found in the serum of approximately 8% of healthy subjects older than age 50, usually in low titer, but often accompanied by related "thyrogastric" autoantibodies.


Intrathecal synthesis of glutamic acid decarboxylase 65 (GAD65) antibody has been demonstrated in patients with stiff-man syndrome, but cerebrospinal fluid (CSF) values are log orders lower than serum. We have not determined the frequency of GAD65 antibodies in spinal fluid of patients with various diagnoses.

Analytic Time

3 days

Day(s) and Time(s) Performed

Monday through Friday; 5 a.m., 2 p.m.

Saturday, Sunday; 7 a.m.

Clinical Reference

1. Saiz A, Arpa J, Sagasta A, et al: Autoantibodies to glutamic acid decarboxylase in three patients with cerebellar ataxia, late-onset insulin-dependent diabetes mellitus and polyendocrine autoimmunity. Neurology 1997 October;49(4):1026-1030

2. Boylan KB, Lennon VA: Cerebellar ataxia with glutamic acid decarboxylase antibody. Ann Neurol 1999;46:457 (abstract)

3. Dalakas MC, Li M, Fujii M, Jacobowitz DM: Stiff person syndrome: quantification, specificity, and intrathecal synthesis of GAD65 antibodies. Neurology 2001 September 11;57:780-7844. McKeon A, Pittock SJ: Paraneoplastic encephalomyelopathies: pathology and mechanisms. Acta Neuropathol 2011;122:381-400

Method Name

Radioimmunoassay (RIA)

Specimen Type


Specimen Required

Container/Tube: Sterile vial

Specimen Volume: 1.5 mL

Specimen Minimum Volume

1 mL

Specimen Stability Information

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

Reference Values

≤0.02 nmol/L

Reference values apply to all ages.

Test Classification

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

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
GD65C GAD65 Ab Assay, CSF 94359-7


Result ID Test Result Name Result LOINC Value
21702 GAD65 Ab Assay, CSF 94359-7


If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Behavioral, mml-Epilepsy, mml-Movement-Disorders, mml-Demyelinating-Diseases, mml-Neuroimmunology, mml-Neuromuscular, mml-Pediatric, mml-Spinal-Cord, mml-Neuro-ophthalmology