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Test Directory - GAD Antibody

Synonyms

Glutamic Acid Decarboxylase (GAD) Antibody

Clinical Indications

GAD is involved in the control of release of insulin. However, it is not pancreatic B-cell specific and is found in cerebellum, sympathetic ganglia and the testis.
Different epitopes of GAD antibodies have been described in association with Type 1 DM  and 'stiff man syndrome'. In assessment of asymptomatic, high risk, population the presence of antibodies to GAD (or islet cell or insulin) are associated with high incidence of onset of Type 1 diabetes  within 5 to 7 years. 'Stiff man syndrome' may be associated with malignancy (paraneoplastic disease) and is characterised by muscle rigidity and spasm. There is little evidence for use of GAD antibodies in monitoring disease progression.
The assay detects GAD antibodies present in both Type 1 DM and 'stiff man syndrome'.

Request Form

Combined Pathology Blood form (Yellow/Black)

Availability

Analysed by referral laboratory if specific criteria met.

Protein Ref. Unit, Northern General Sheffield Hospital.

Specific Criteria

Requested by Consultant (Endocrinologist, Rheumatologist, Neurologist) or agreed with Consultant Biochemist.

Turnaround Time

1 month

Specimen

Serum

Volume

2 ml

Container

Yellow top (SST) tube

Lab. Handling

Aliquot and store at 4C

Causes for Rejection

Not meeting specific criteria.

Interpretation

'Stiff man' syndrome: GAD antibody is present in over 90% of patients with slow, progressive disease of all muscles that eventually stabilises and 20% of patients with rigidity and spasm restricted to distal muscles (e.g. leg). Patients with acute progressive disease are GAD antibody negative.
Type 1 diabetes: 70 - 80% of patients with type 1 diabetes show positive GAD antibodies although these disappear as the disease progresses.

        

 


Last edited 16/04/14