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Glutamic Acid Decarboxylase (GAD) Autoantibody
This test is intended for the semiquantitative determination of glutamic acid decarboxylase (GAD) antibody in human serum; it is useful as an aid in the diagnosis of type 1 diabetes mellitus (autoimmune mediated diabetes).1
Enzyme-linked immunosorbent assay (ELISA)
Pediatric and adult: 0.0−5.0 units/mL
This test allows for the detection of the presence of antibodies to glutamic acid decarboxylase, which provides early evidence of autoimmune disease activity; its measurement has been shown to be useful in assisting the physician in the prediction, diagnosis, and management of patients with diabetes.2-6
Glutamic acid decarboxylase (GAD65) is an enzyme that is produced primarily by pancreatic islet cells. A number of recent studies indicate that patients with insulin-dependent diabetes mellitus (IDDM) often have antibodies to GAD65 and several other islet cell antigens.7 This is consistent with the hypothesis that IDDM is an autoimmune disease and that autoantibody production is an early step in the development of IDDM.8 Autoantibodies can be detected in many cases prior to the onset of glucose intolerance. The presence of GAD65 autoantibodies can be detected in many cases prior to the onset of glucose intolerance. The presence of GAD65 autoantibodies has been shown to be a strong predictive marker for the eventual onset of IDDM. Measurement of GAD65 antibody can also be of use in distinguishing insulin-dependent from non−insulin-dependent diabetics when the clinical history is ambiguous. GAD65 autoantibodies are often markedly elevated in patients with the stiff-person syndrome (also referred to as stiff-man syndrome), a condition that is associated with fluctuating stiffness and paroxysmal spasms of the trunk and legs.9,10
0.4 mL (Note: This volume does not allow for repeat testing.)
Red-top tube or gel-barrier tube
If a red-top tube is used, transfer separated serum to a plastic transport tube. Avoid hemolysis.
Causes for Rejection
Nonserum sample; grossly hemolyzed or lipemic sample
This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
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