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GAD 65 Antibody by IFA (for Paraneoplastic syndrome)
Immunity
Report in 48Hrs
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No Fasting Required
Details
It helps identify autoimmune neurologic disorders, type 1 diabetes, and certain paraneoplastic syndromes
₹8,190₹9,980
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GAD 65 Antibody by IFA (for Paraneoplastic syndrome)
- Why is it done?
- Detects circulating antibodies against glutamic acid decarboxylase 65 (GAD 65), a neurotransmitter-synthesizing enzyme found in the nervous system
- Diagnoses paraneoplastic neurological syndromes (PNS), which are autoimmune neurological disorders triggered by malignant tumors
- Identifies autoimmune neurological conditions including cerebellar ataxia, limbic encephalitis, stiff-person syndrome, and other movement disorders
- Performed when patients present with unexplained neurological symptoms concurrent with or preceding cancer diagnosis
- Typically ordered during initial neurological workup when paraneoplastic syndrome is clinically suspected
- Normal Range
- Normal/Negative Result: Less than 0.02 nmol/L or absent antibodies (exact cutoff values may vary by laboratory)
- Borderline/Equivocal Result: 0.02-0.05 nmol/L (may require repeat testing or additional investigation)
- Positive Result: Greater than 0.05 nmol/L or clearly present on immunofluorescence assay
- Units of Measurement: nmol/L (nanomoles per liter) or as a titer in immunofluorescence assay
- Normal Result Interpretation: Absence of anti-GAD 65 antibodies, making paraneoplastic neurological syndrome less likely (though does not completely exclude it)
- Abnormal Result Interpretation: Presence of anti-GAD 65 antibodies indicates autoimmune neurological disorder, strongly suggesting paraneoplastic syndrome and necessitating cancer screening
- Interpretation
- Negative Result (<0.02 nmol/L): Rules out GAD 65-associated paraneoplastic syndrome; alternative diagnoses should be considered including other autoimmune, infectious, or metabolic causes
- Low-Positive Result (0.05-0.10 nmol/L): Suggests GAD 65-associated autoimmunity; may indicate paraneoplastic syndrome or autoimmune neurological disease; clinical correlation and imaging studies recommended
- High-Positive Result (>0.10 nmol/L): Strongly indicates GAD 65-mediated autoimmune disorder, particularly paraneoplastic syndrome; urgent oncological screening warranted
- High-Titer IFA Pattern: Strong intracellular or cytoplasmic fluorescence pattern indicates robust autoimmune response and higher likelihood of active neurological disease
- Factors Affecting Results: False negatives may occur in early disease; seropositive status does not establish temporal relationship to cancer; concurrent testing for other paraneoplastic antibodies (CRMP5, Hu, Yo) may increase diagnostic yield
- Clinical Significance: GAD 65 antibodies found in 5-10% of paraneoplastic cerebellar ataxia cases and associated with small cell lung cancer (SCLC), Hodgkin lymphoma, and breast cancer
- Longitudinal Changes: Antibody titers may correlate with disease activity; response to cancer treatment often parallels improvement in neurological symptoms
- Associated Organs
- Central Nervous System (Primary): Cerebellum (cerebellar ataxia), cerebral cortex (limbic encephalitis), brainstem, and spinal cord
- Peripheral Nervous System: Motor neurons (stiff-person syndrome), sensory nerves, and neuromuscular junction
- Malignant Tumors Most Commonly Associated: Small cell lung cancer (SCLC), Hodgkin lymphoma, breast cancer, ovarian cancer, and gastric cancer
- Primary Disorders Associated: Cerebellar ataxia (most common), limbic encephalitis, stiff-person syndrome, progressive encephalomyelitis with rigidity, and ataxia
- Potential Complications of Abnormal Results: Severe neurological disability including ataxia, cognitive decline, seizures, autonomic dysfunction, and death if untreated
- Risks Associated with Paraneoplastic Syndrome: Progressive neurological deterioration may occur before cancer diagnosis; some patients develop resistant neurological symptoms despite cancer remission
- Secondary Effects: Elevated risk of mortality; increased healthcare burden; potential for delayed cancer diagnosis; significant morbidity from neurological impairment
- Follow-up Tests
- Additional Paraneoplastic Antibody Panel: Testing for anti-CRMP5 (CV2), anti-Hu (ANNA-1), anti-Yo (PCA-1), anti-Ri (ANNA-2), and anti-Amphiphysin antibodies if initial GAD 65 is negative
- Comprehensive Malignancy Screening: CT chest/abdomen/pelvis, whole-body PET scan, age-appropriate cancer screening (mammography for women, PSA for men)
- Neuroimaging Studies: Brain MRI with contrast to evaluate for limbic encephalitis, cerebellar atrophy, or other structural abnormalities; spinal MRI if spinal cord involvement suspected
- Cerebrospinal Fluid (CSF) Analysis: CSF protein, glucose, cell count, IgG index, oligoclonal bands, and viral studies to assess for CNS inflammation and alternative diagnoses
- Electrophysiological Studies: Electromyography (EMG) and nerve conduction studies (NCS) to characterize peripheral nervous system involvement
- EEG and Evoked Potentials: Electroencephalography and brainstem/somatosensory evoked potentials to document central nervous system dysfunction
- Follow-up GAD 65 Testing: Serial antibody testing at 3-6 month intervals to monitor disease activity and treatment response
- Imaging Surveillance: Periodic imaging at baseline and during follow-up to assess for emerging or recurrent malignancy (frequency depends on initial cancer findings)
- Recommended Monitoring Frequency: Initial intensive evaluation with tests within 1-2 weeks; follow-up assessments at 4-8 weeks; then quarterly or biannually depending on clinical course
- Fasting Required?
- Fasting Required: No
- Dietary Restrictions: No fasting or dietary restrictions necessary for this serological test
- Medications: No medications require discontinuation; continue all regularly prescribed medications
- Blood Draw Timing: Can be performed at any time of day; no time-dependent variations expected
- Patient Preparation: Patient should be calm and seated for 5-10 minutes before blood draw; ensure adequate hydration
- Sample Collection: 5-10 mL of serum in appropriate tube; can also use plasma or cerebrospinal fluid if ordered
- Sample Handling: Keep at room temperature or refrigerated (2-8°C) until processing; do not freeze unless long-term storage required
- Turnaround Time: Typically 5-7 business days; may be expedited to 2-3 days if urgent paraneoplastic syndrome suspected
How our test process works!
