GAD Total Antibody
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This test detects all circulating GAD autoantibodies, regardless of method (ELISA, RIA, or IFA)
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🧪 What is GAD Total Antibody?
GAD (Glutamic Acid Decarboxylase) Total Antibody refers to autoantibodies directed against GAD enzyme, especially the GAD65 isoform (and occasionally GAD67). GAD is crucial in converting glutamate to GABA, an inhibitory neurotransmitter in the brain.
This test detects all circulating GAD autoantibodies, regardless of method (ELISA, RIA, or IFA) and is commonly used for:
- Diagnosing autoimmune diabetes (especially latent or early-onset type 1)
- Identifying neurological autoimmune disorders
- Screening for paraneoplastic syndromes
❓ Why is the Test Done?
To:
- Identify Type 1 Diabetes Mellitus (T1DM) or Latent Autoimmune Diabetes in Adults (LADA)
- Evaluate stiff-person syndrome, autoimmune epilepsy, or autoimmune encephalitis
- Investigate paraneoplastic neurologic syndromes
- Differentiate autoimmune diabetes from Type 2 Diabetes
📊 Normal Range
Result | Interpretation |
|---|---|
Negative | < 5 IU/mL (may vary by lab) |
Positive | > 5 IU/mL (suggestive of GAD autoimmunity) |
Labs may report as quantitative values (IU/mL) or qualitative (Positive/Negative/Borderline).
📈 Interpretation of Results
Result | Clinical Meaning |
|---|---|
Negative | No GAD autoimmunity detected |
Low Positive | May indicate early or mild autoimmune process, seen in LADA or early T1DM |
Moderate to High Positive | Suggests autoimmune diabetes, or possibly autoimmune neurologic disorder (e.g., SPS, cerebellar ataxia, limbic encephalitis) |
High + rapid progression to insulin dependency | Strongly supports T1DM or LADA |
🧠 Associated Organs and Conditions
Organ/System | Associated Conditions |
|---|---|
Pancreas | - Type 1 Diabetes |
CNS (brain/spinal cord) | - Stiff-person syndrome |
Cancer-Associated (Paraneoplastic) | Small cell lung cancer, thymoma, breast cancer (rare) |
🔄 Related / Follow-Up Tests
- Other Islet Autoantibodies:
- IA-2, ZnT8, Insulin autoantibodies (IAA) – In T1DM diagnosis
- C-peptide – To assess endogenous insulin production
- HbA1c, Fasting glucose – For glycemic status
- MRI brain/CSF analysis – If neurological symptoms present
- Other paraneoplastic antibodies – Anti-Hu, Anti-Yo, etc.
- Thyroid antibodies (Anti-TPO) – Autoimmune overlap common
✅ Fasting Required?
Test | Fasting Required |
|---|---|
GAD Total Antibody | ❌ No fasting required — Can be done anytime |
📝 Summary
Parameter | Summary |
|---|---|
What | Detects autoantibodies against GAD enzyme (esp. GAD65) |
Why Test | Diagnose or confirm autoimmune diabetes, stiff-person syndrome, paraneoplastic syndrome |
Normal Range | < 5 IU/mL (Negative) |
Positive Result | Suggests GAD autoimmunity, especially in T1DM, LADA, or neurologic disorders |
Follow-up Tests | Islet antibodies, C-peptide, HbA1c, MRI/CSF (neurologic cases) |
Fasting Required | ❌ No |
How our test process works!
