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PTD - 236

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  (GAD65) and 'stiff man syndrome' (GAD65 and GAD67). 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 Protein Reference Unit, Sheffield if specific criteria met.

Specific Criteria

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

Patient Preparation

None required.

Turnaround Time

1 month

Specimen

Serum

Volume

2 ml

Container


Yellow top (SST) tube or


Paediatric orange top (lithium-heparin)

Causes for Rejection

Not meeting specific criteria.

Interpretation

'Stiff man' syndrome: GAD antibodies are 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 (GAD65) although these disappear as the disease progresses.

Lab. Handling

Processing: Aliquot (MPA) and store at 4C in separating fridge (CB39). Referral: GAD and send or NOGAD and save in separating freezer (CB40) at -20C, saved frozen rack.


Version 1.0 / May 2014                                                                                                           Approved by: Consultant Biochemist