Anti-GBM antibody (Anti-Glomerular basement membrane antibody), Good Pasture Syndrome
Sample for Anti-GBM antibody
- This test is done on the venous blood to get the serum.
- The patient needs to fast for 8 hours.
- Another sample is a tissue biopsy of the kidney and lung tissue. It is used for microscopic evaluation.
Purpose of the test (Indications) for Anti-GBM antibody
- To diagnose autoimmune-induced glomerulonephritis.
- To differentiate from the other type of glomerulonephritis.
- To diagnose Goodpasture’s syndrome.
Precaution for Anti-GBM antibody
- Drugs like antibiotics may decrease the test result.
Pathophysiology of Anti-GBM glomerulonephritis
- This is an autoimmune phenomenon.
- About 5% of glomerulonephritis is Anti-GBM type.
- Some autoantibodies react with the basement membrane of the renal glomeruli capillaries.
- These autoantibodies react with small blood vessels of the kidney and lung.
- These autoantibodies react with pulmonary alveoli.
- When these antibodies react only with the glomeruli basement, they produce anti-GBM glomerulonephritis.
- In Goodpastaur syndrome, there are circulating antibodies against the glomerular basement membrane. These antibodies also react against the alveoli of the lung.
The mechanism of the tissue damage:
- It is a type III hypersensitivity reaction where immune complexes activate the complement system.
- Immune complexes give rise to:
- Glomerulonephritis leads to hematuria.
- Pulmonary hemorrhage leads to hemoptysis.
- Positive autoantibodies against basement membranes.
- This hypersensitivity reaction is complement-mediated.
- The damage is due to the deposition of immune complexes.
- It is an autoimmune disease characterized by the following:
- When both kidneys and lungs are involved.
- Hemoptysis (pulmonary hemorrhage).
- Antibodies react to the kidneys and lungs’ basement membrane (antigen).
- Both kidneys and lungs are involved in 60% to 70 % of cases (Goodpasture syndrome).
- 20% to 40 % of the cases show only involvement of the kidneys, only then called anti-GBM glomerulonephritis.
- The patient will have blood in a cough when the lungs are involved.
Diagnosis of Anti-GBM glomerulonephritis and Goodpasture syndrome:
- The serum method is easier, faster, and more reliable for patients with a difficult or contraindicated biopsy.
- Blood by enzyme immunoassay (EIA):
- Negative = <20 units
- Borderline = 20 to 100 units
- Positive = >100 units
- The high anti-GBM titer is suggestive of the following:
- Goodpasture’s syndrome.
- Lupus erythematosus.
- Anti-GBM nephritis.
- Lung or renal biopsy demonstrates these antibodies by immunohistochemical technique.
Normal anti-GMB antibody
Blood (EIA enzymatic immunoassay):
- Negative = <20 units.
- Borderline = 20 to 100 units.
- Positive = >100 units.
- Negative = No immunofluorescence was seen on renal or lung biopsy.
- Negative = <5 EU/mL by ELIZA
- Borderline = 5.1 to 20.0 EU/mL
- Positive = 20.1 to 400 EU/mL
- A negative result does not rule out Goodpasture’s syndrome.
Anti-GBM antibody seen in:
- Autoimmune glomerulonephritis.
- Goodpasture’s syndrome.
- Tubulointerstitial nephritis.
- Some patients with lupus nephritis.
Questions and answers:
Question 1: What is the criteria for Goodpasture syndrome.
There is the involvement of the lungs and kidneys.
Question 2: What is the significance of anti-GBM antibody.
It diagnoses anti-GMB glomerulonephritis and Good pasture syndrome.