What is the Aquaporin-4 Antibodies Test?

The Aquaporin-4 (AQP4) Antibodies Test measures the presence of IgG antibodies targeting aquaporin-4 water channels found on astrocytes (cells within the central nervous system). These antibodies are highly specific markers for Neuromyelitis Optica Spectrum Disorder (NMOSD), a rare autoimmune neurological disease that primarily affects the optic nerves (causing optic neuritis) and the spinal cord (causing transverse myelitis).

NMOSD often mimics multiple sclerosis (MS) but requires different management and treatment, making accurate antibody testing essential for diagnosis. Detection of AQP4-IgG confirms NMOSD in approximately 70–80% of cases.

At London Blood Tests, this assay is performed using cell-based indirect immunofluorescence or ELISA, depending on clinical indication, to ensure sensitivity and specificity in alignment with UK neuroimmunology standards.

Benefits of the Aquaporin-4 Antibodies Test

• Highly Specific for NMOSD
  Detects antibodies directly linked to Neuromyelitis Optica Spectrum Disorder, differentiating it from multiple sclerosis and other demyelinating diseases.

• Supports Early Diagnosis
  Early detection helps prevent irreversible vision or spinal cord damage through timely initiation of immunotherapy.

• Guides Treatment Decisions
  Helps neurologists determine whether immunosuppressive therapy (e.g., rituximab or steroids) is indicated.

• Monitors Disease Activity
  In some cases, antibody levels may help monitor disease progression or relapse risk.

• Reduces Misdiagnosis
  Avoids misclassification as MS, ensuring patients receive appropriate and potentially sight-saving treatment.

• Useful in AQP4-Negative Cases
  Supports further investigation into MOG (Myelin Oligodendrocyte Glycoprotein) antibodies when AQP4 is negative but NMOSD is suspected.

• Optional GP Consultation
  Results can be reviewed by a GP for further referral to a neurologist or neuroimmunology specialist if needed.

Why Do I Need an Aquaporin-4 Antibodies Test?

You may require this test if your clinician suspects Neuromyelitis Optica Spectrum Disorder (NMOSD) or other autoimmune demyelinating conditions.
Common reasons include:

• Vision loss in one or both eyes (optic neuritis)
• Weakness or numbness in limbs due to spinal cord inflammation
• Frequent vomiting or hiccups (area postrema involvement)
• Bladder or bowel dysfunction
• Recurrent attacks suggestive of demyelination without clear MS diagnosis
• MRI findings atypical for multiple sclerosis

This test helps confirm a diagnosis and guide long-term immunosuppressive therapy.

Step-by-Step: How the Test Works

In-Clinic Testing at London Blood Tests

1. Book Your Appointment
• Appointments can be booked online or by phone, no referral required.
• You’ll receive instructions and pre-test guidance before your visit.
2. Sample Collection
• A venous blood sample (serum) is collected by an experienced phlebotomist.
• The procedure takes approximately 10 minutes.
3. Laboratory Processing
• The sample is sent to a UKAS-accredited neuroimmunology laboratory for analysis.
• Testing is performed using a cell-based assay (CBA) or ELISA to detect AQP4-IgG antibodies.
4. Quality Control
• Positive or borderline samples are confirmed via secondary immunofluorescence to ensure accuracy.
5. Results Delivery
• Results are typically ready within 10 business days, securely available through our online portal.
6. Optional GP Consultation
• A GP can review your results and refer you to a neurologist if further evaluation is indicated.

At-Home Blood Draw (UK-Wide Service)

1. Book Your Appointment – Schedule a phlebotomist home or hotel visit online or by phone.
2. Phlebotomist Visit – A certified phlebotomist arrives at your location to collect a venous blood sample.
3. Sample Handling – The sample is safely packaged and couriered to our UKAS-accredited laboratory the same day.
4. Laboratory Testing – The lab performs cell-based immunoassay or ELISA to detect AQP4 antibodies.
5. Results Delivery – Receive your secure report online within 10 business days.
6. Optional GP Consultation – Discuss your results with a GP for interpretation and onward specialist referral if needed.

Your Aquaporin-4 Antibodies Test Results – Explained

Results are typically reported as positive, negative, or borderline for AQP4-IgG antibodies.

Interpretation:

• Negative: No AQP4 antibodies detected. NMOSD is less likely, though MOG antibody testing may be considered.
• Borderline: Low-level antibodies; may require repeat testing or correlation with MRI findings.
• Positive: Confirms presence of AQP4-IgG, highly specific for Neuromyelitis Optica Spectrum Disorder.

Typical sensitivity and specificity:

• Sensitivity: ~70–80% for NMOSD
• Specificity: >99% compared to MS and other autoimmune disorders

A positive result supports immediate neurological referral. Results should always be interpreted in conjunction with clinical presentation, MRI, and cerebrospinal fluid findings.