Glutamic Acid Decarboxylase-65 (GAD65) Antibody Test
The Glutamic Acid Decarboxylase-65 (GAD65) Antibody test measures antibodies against the GAD65 protein in a serum sample. Quest describes it as a marker used in evaluating type 1 diabetes, including distinguishing it from type 2 diabetes and related autoimmune conditions.
About this test
GAD65 is a protein that the immune system targets in type 1 diabetes, and Quest lists it as a key marker of the disease. This test measures antibodies against GAD65 in a serum sample, using an Enzyme Linked Immunosorbent Assay.
Quest lists several situations where this test may be ordered: to screen for presymptomatic type 1 diabetes in people with a family history or a high-risk HLA genotype, to help distinguish type 1 diabetes from type 2 diabetes and atypical forms such as LADA, and to help confirm diagnoses of stiff-man syndrome.
Who might consider this test?
- Often being evaluated for a form of diabetes where the type is unclear
- Have a family history that raises the question of presymptomatic type 1 diabetes
- Are part of a stiff-man syndrome evaluation
Test details
| Quest code | 34878 |
|---|---|
| Methodology | Enzyme Linked Immunosorbent Assay |
| Sample type | 1 mL serum |
| Collection | Quest patient service center |
Reference range
<5 IU/mL
Reference ranges are general guidance. The range printed on your own laboratory report is the one that applies to your result.
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Quest resources
Additional details
What this test looks at
The test reports one value: the level of GAD65 antibody in a 1 mL serum sample, measured by ELISA.
How it's often used alongside other tests
Quest notes that professional guidelines call for testing at least two islet autoantibodies to identify presymptomatic stages of type 1 diabetes, so relying on GAD65 alone limits diagnostic accuracy. For that reason, a clinician may order it together with other islet autoantibody tests rather than as a standalone result.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does the GAD65 Antibody test measure?
It measures levels of antibodies against glutamic acid decarboxylase (GAD65), a protein the immune system targets in type 1 diabetes, using an Enzyme Linked Immunosorbent Assay on a serum sample.
How is the sample collected?
The test uses a 1 mL serum sample from a routine blood draw at a Quest Diagnostics patient service center.
Do I need to prepare for this test?
No preparation instructions are listed for this test, though people follow any instructions their ordering clinician provides.
Why might this test be ordered?
Quest lists screening for presymptomatic type 1 diabetes in people with a family history or high-risk genotype, distinguishing type 1 from type 2 diabetes and atypical forms such as LADA, and helping confirm stiff-man syndrome as reasons this test may be ordered.
Can a GAD65 result alone confirm type 1 diabetes?
No. Quest notes that professional guidelines call for testing more than one islet autoantibody to identify presymptomatic stages, so this result is read by a clinician alongside other markers and the clinical picture.
What does a Glutamic Acid Decarboxylase-65 Antibody test cost without insurance?
$355. Celio Health's price is a flat cash price and insurance is never billed: the required physician's order is included.