Glutamic Acid Decarboxylase (GAD) Autoantibody Blood Test

Quick Facts

• Sample: Blood serum
• Fasting: Not required
• Turn-around: 4–8 business days. May take longer based on weather, holiday, or lab delays.

Benefits

• Early autoimmune diabetes detection - Identify type 1 diabetes risk years before symptoms appear 
• Accurate diabetes classification - Distinguish type 1 from type 2 diabetes for proper treatment 
• No fasting required - Convenient testing with minimal preparation needed 
• Quick results - Get answers in just 4-8 days from sample collection 
• Confidential screening - Order online without needing a doctor's visit first 
• Neurological condition support - Helps diagnose stiff-person syndrome and related autoimmune disorders

Who Is This Test For?

• Adults with new-onset diabetes needing type classification 
• Individuals with ambiguous diabetes symptoms requiring clarification 
• People with family history of type 1 diabetes or autoimmune conditions 
• Adults over 30 with non-obese diabetes presentation (possible LADA) 
• Patients with neurological symptoms suggestive of stiff-person syndrome 
• Those seeking proactive health screening for autoimmune diabetes risk

How It Works – Just 3 Steps

1. Order online and visit any lab location for a simple blood draw
2. Lab analysis measures GAD65 autoantibodies using advanced immunoassay technology
3. Receive results within 4-8 business days

FAQ

What are GAD autoantibodies? Antibodies that attack the GAD enzyme in pancreatic cells, indicating autoimmune destruction of insulin-producing cells.

Can this test detect type 2 diabetes? No, GAD antibodies are not present in type 2 diabetes; they specifically indicate autoimmune diabetes.

How accurate is this test? Detects antibodies in approximately 70-80% of type 1 diabetes cases and >90% of stiff-person syndrome patients.

Do I need to fast for this test? No fasting required, but stop biotin supplements 72 hours before testing to avoid interference.

What if my results are negative? Negative results reduce likelihood of autoimmune diabetes but don't completely exclude it; additional testing may be recommended.

How long do results take? Typically 4-8 business days.

More Details

What is the purpose of this test?

The GAD autoantibody test detects antibodies against glutamic acid decarboxylase enzyme, primarily GAD65, which is found in pancreatic islet cells and the nervous system. This enzyme is crucial for insulin regulation through its role in producing the neurotransmitter GABA. The presence of GAD autoantibodies indicates an autoimmune response targeting pancreatic cells, which is a hallmark of type 1 diabetes mellitus and latent autoimmune diabetes in adults (LADA) (Mayo Clinic 2025).

Who would benefit from this test?

This test is especially valuable for individuals with new or unclear diabetes diagnosis, adults suspected of having LADA, patients with neurological symptoms suggestive of stiff-person syndrome, and those at risk for autoimmune diabetes. It's particularly useful for adults over 30 with a non-obese phenotype who develop diabetes, as this presentation often indicates autoimmune rather than typical type 2 diabetes (Diabetes.co.uk 2023).

When should I order this test?

Order this test when diabetes type is uncertain, especially in adults over 30 with non-obese phenotype, or to assess autoimmune activity in known or suspected type 1 diabetes or LADA. It's also indicated when neurological symptoms suggest stiff-person syndrome or other autoimmune conditions affecting the nervous system (NICE NG17 2021).

How do I interpret the results?

Negative (<10 IU/ml)

• What it means: No significant autoimmune activity detected
• Typical action: Reduces likelihood of autoimmune diabetes

Positive (>10 IU/ml)

• What it means: Autoimmune response present
• Typical action: Suggests type 1 diabetes or LADA

Strongly positive (>100 IU/ml)

• What it means: High autoimmune activity
• Typical action: Strong indication for insulin therapy

The presence of two or more islet autoantibodies, including GAD, significantly increases specificity for predicting type 1 diabetes development.

Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.

Pre-test preparation

No fasting is required for this test. However, you should stop taking biotin supplements at least 72 hours before sample collection to prevent assay interference. Blood is drawn into a serum separator tube and shipped to the lab under standard conditions (Labcorp 2011).

How often should I get tested?

• Initial diabetes diagnosis: Once for classification
• Monitoring known autoimmune diabetes: Annually or as directed
• Family history screening: Every 2-3 years
• Negative result with high suspicion: Repeat in 6-12 months

Why early detection matters

Early detection of GAD autoantibodies can predict onset of type 1 diabetes years before clinical symptoms appear, allowing for earlier intervention and better outcomes. Approximately 70-80% of patients with type 1 diabetes have detectable GAD autoantibodies at or before diagnosis (PMC 2020). This early identification enables timely insulin therapy initiation and reduces risk of diabetic complications.

Related tests you may consider

Antipancreatic Islet Cells Serum Test - Detects autoantibodies targeting pancreatic islet cells, which may be present in autoimmune diabetes. May complement other markers such as GAD antibodies for a comprehensive autoimmune diabetes assessment.

Insulin Autoantibodies (IAA) Test - Useful for confirming autoimmune diabetes, especially in early disease stages.

C-Peptide Test - Measures endogenous insulin production to differentiate type 1 from type 2 diabetes and assess beta-cell function.