Glomerular Basement Membrane (GBM) Antibody

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Autoantibody to GBM.

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Glomerular Basement Membrane (GBM) Antibody Test Guide

Why is it done?
- Detects autoantibodies directed against the alpha-3 chain of type IV collagen found in the glomerular basement membrane of the kidneys
- Diagnoses anti-GBM disease (Goodpasture syndrome), an autoimmune disorder causing rapidly progressive glomerulonephritis and pulmonary hemorrhage
- Ordered when patients present with hematuria, proteinuria, acute kidney injury, or concurrent pulmonary-renal manifestations
- Used to differentiate anti-GBM disease from other causes of rapidly progressive glomerulonephritis such as ANCA-associated vasculitis or immune complex disease
- Performed urgently in suspected cases to enable rapid diagnosis and initiation of aggressive immunosuppressive therapy to preserve renal function
- May be used for monitoring disease activity and treatment response in confirmed anti-GBM disease cases
Normal Range
- Normal Result: Negative or <1.0 EU/mL (ELISA method)
- Negative or Absent IgG antibodies against GBM antigens (Immunoassay or Radioimmunoassay)
- Interpretation of Negative: No detectable anti-GBM antibodies present; anti-GBM disease is ruled out or not active
- Positive Result: ≥1.0 EU/mL or Higher
- Detectable IgG antibodies against GBM antigens indicating active or recent anti-GBM disease
- Borderline/Equivocal Values: Results in the range of 0.8-1.2 EU/mL may warrant repeat testing or additional diagnostic confirmation
- Units: EU/mL (ELISA Units), or reported as positive/negative or as a semiquantitative result depending on laboratory methodology
- Clinical Significance: A positive test strongly suggests anti-GBM disease when clinical presentation is consistent; negative results reduce likelihood but do not completely exclude the diagnosis if clinical suspicion remains high
Interpretation
- Positive GBM Antibody Result: Confirms anti-GBM disease; patient likely has anti-GBM-mediated glomerulonephritis with high probability of rapid renal decline if untreated
- High Antibody Titers: Associated with more severe renal and pulmonary involvement; correlate with disease activity and may predict worse clinical outcomes
- Negative GBM Antibody with Clinical Suspicion: Serologic anti-GBM disease is unlikely; kidney biopsy with direct immunofluorescence is warranted to assess for linear IgG deposition along GBM, which may reveal anti-GBM disease not detected by serology
- Serial Antibody Monitoring: Declining titers suggest treatment response and improved prognosis; persistently elevated or rising titers may indicate inadequate disease control requiring treatment intensification
- Factors Affecting Results: Stage of disease (early vs. chronic), immunosuppressive therapy, time from symptom onset, presence of pulmonary involvement, and renal function status all influence antibody levels and test interpretation
- Double-Positive Serology: Rarely, patients may have concurrent anti-GBM and ANCA antibodies; requires careful clinical correlation and histologic confirmation
- Clinical Significance Varies With Presentation: Pulmonary-renal syndrome (hemoptysis plus hematuria) with positive serology is highly specific for Goodpasture syndrome; isolated renal presentation requires additional tests for definitive diagnosis
Associated Organs
- Primary Organ Systems Involved:
- Kidneys: Glomerular basement membrane is the primary target; damage leads to glomerulonephritis, hematuria, proteinuria, and rapid decline in glomerular filtration rate
- Lungs: Alveolar basement membrane is also affected; causes alveolar hemorrhage manifesting as hemoptysis, dyspnea, and infiltrates on chest imaging
- Diseases Associated with Abnormal Results:
- Anti-GBM Disease (Goodpasture Syndrome): Autoimmune condition characterized by rapidly progressive glomerulonephritis with or without pulmonary hemorrhage
- Rapidly Progressive Glomerulonephritis (RPGN): Anti-GBM disease accounts for 10-20% of cases; others include ANCA-associated vasculitis and immune complex-mediated RPGN
- Pulmonary-Renal Syndrome: Clinical triad of hemoptysis, hematuria, and renal insufficiency; highly suggestive of Goodpasture syndrome when anti-GBM antibodies are present
- Potential Complications of Abnormal Results:
- End-Stage Renal Disease: Without prompt treatment, anti-GBM disease leads to irreversible renal failure within weeks to months; may require dialysis or transplantation
- Acute Respiratory Distress: Massive pulmonary hemorrhage can cause life-threatening hypoxemia and respiratory failure, particularly early in disease course
- Cardiovascular Complications: Secondary hypertension from renal involvement; fluid overload and pulmonary edema from renal dysfunction
- Chronic Organ Dysfunction: Even with treatment, chronic kidney disease and pulmonary fibrosis may persist; recurrent disease possible after renal transplantation
Follow-up Tests
- Confirmatory and Diagnostic Tests:
- Kidney Biopsy with Direct Immunofluorescence: Gold standard for diagnosis; shows linear IgG deposition along glomerular basement membrane; performed when serology is negative but clinical suspicion remains high
- ANCA Serology (c-ANCA/p-ANCA): Excludes ANCA-associated vasculitis; important for differential diagnosis of rapidly progressive glomerulonephritis
- Circulating Immune Complex Testing: Evaluates for immune complex-mediated glomerulonephritis as alternative diagnosis
- Renal Function Assessment:
- Serum Creatinine and Blood Urea Nitrogen (BUN): Baseline and serial monitoring to assess renal function decline; essential for treatment decisions and prognostication
- Glomerular Filtration Rate (GFR): Calculated from creatinine; determines severity of renal impairment and dialysis requirement
- Urinalysis: Shows hematuria and proteinuria; helps assess disease activity and monitor treatment response
- Pulmonary Assessment:
- Chest X-ray or High-Resolution CT: Evaluates for alveolar hemorrhage, infiltrates, and pulmonary involvement; initial imaging and periodic follow-up
- Pulmonary Function Tests: Assesses diffusion capacity (DLCO) for alveolar hemorrhage; baseline and during treatment monitoring
- Disease Activity and Treatment Monitoring:
- Repeat GBM Antibody Testing: Performed serially during treatment (initially weekly to monthly) to assess treatment response; declining titers correlate with clinical improvement
- Complete Blood Count: Monitors for cytopenias related to immunosuppressive therapy; baseline and periodic surveillance
- Liver Function Tests: Assesses hepatic toxicity from immunosuppressive agents; baseline and ongoing surveillance
- Monitoring Frequency:
- Active Phase (Initial 3-6 months): Weekly to biweekly GBM antibody testing, renal function, and urinalysis; frequent imaging and clinical assessment
- Maintenance Phase (6-12 months): Monthly to quarterly GBM antibody testing; monthly renal function and urinalysis; semi-annual imaging
- Long-term Follow-up: Quarterly to annual testing; indefinite monitoring recommended given risk of relapse, particularly after immunosuppressive therapy discontinuation
Fasting Required?
- Fasting Requirement: No
- Food and fluid intake do not affect GBM antibody detection; fasting is not necessary for this test
- Sample Collection Requirements:
- Venipuncture to collect serum sample, typically 5-10 mL of blood in a clot-activating tube (SST or similar)
- Sample must be allowed to clot at room temperature, then centrifuged to separate serum
- Serum should be refrigerated or frozen if testing is delayed; samples should be transported on ice or frozen packs if sent to reference laboratory
- Medications to Continue or Avoid:
- No medications need to be held or adjusted specifically for this test
- Immunosuppressive therapy (if already initiated) should continue as prescribed; these medications do not interfere with serum antibody detection
- Steroids, cyclophosphamide, mycophenolate, and other immunosuppressive agents do not interfere with the assay
- Additional Patient Preparation:
- No special preparation required; patient should wear loose-fitting clothing on the arm where blood will be drawn
- Patients should be seated or recumbent during phlebotomy to minimize risk of syncope
- Stress reduction may be helpful; anxiety does not affect antibody results but can reduce drawing complications
- Timing of sample collection in relation to symptom onset is important; earlier samples may have higher positivity rates in acute disease
- Due to high mortality risk in untreated anti-GBM disease, testing should be ordered urgently and expedited in suspected cases; results should be communicated immediately

How our test process works!