Anti-Glomerular basement membrane antibody (Anti-GBM antibody)

Sample
- 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 (lung tissue).
Purpose of the test (Indications)
- To diagnose autoimmune induced glomerulonephritis.
- To differentiate from the other type of glomerulonephritis.
- To diagnose Goodpasture’s syndrome.
Precaution
- Drugs like antibiotics may decrease the test result.
Pathophysiology
- This is an autoimmune phenomenon.
- About 5% of the glomerulonephritis is Anti-GBM type.
- There are auto-antibodies which 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 glomeruli basement then give rise to anti-GBM glomerulonephritis.
- Mechanism of the tissue damage is a type III hypersensitivity reaction where immune complexes activate the complement system.
- Immune complexes give rise to:
- Glomerulonephritis which leads to hematuria.
- Pulmonary hemorrhage leads to hemoptysis.
- Positive autoantibodies against basement membranes.
- Immune complexes give rise to:
- This hypersensitivity reaction is complement-mediated.
- The damage is due to the deposition of immune complexes.
- Goodpasture’s syndrome is autoimmune diseases and characterized by:
- When both kidney and lung are involved.
- Hematuria.
- hemoptysis (pulmonary hemorrhage).
- Antibodies to the basement membrane which acts as an antigen.
- 60 to 70 % of the cases, both kidney, and lung are involved (Goodpasture’s syndrome).
- 20 to 40 % of the cases show the only involvement of the kidneys only then called anti-GBM glomerulonephritis.
- When there is the involvement of the lung, the patient will have blood in a cough.
Diagnosis
- The serum method is easy and faster and more reliable in patients where biopsy is difficult or contraindicated.
- The high anti-GBM titer is suggestive of :
- Goodpasture’s syndrome.
- Lupus erythematosus.
- Anti-GBM nephritis.
- Lung or renal biopsy demonstrates these antibodies by immunohistochemical technique.
Normal
Source 2
Blood (EIA enzymatic immunoassay):
- Negative = <20 units.
- Borderline = 20 to 100 units.
- Positive = >100 units.
Tissue biopsy:
- Negative = No immunofluorescence was seen on renal or lung biopsy.
Source 4
- Negative = <5 EU/mL by ELIZA
- Borderline = 5.1 to 20.0 EU/mL
- Positive = 20.1 to 400 EU/mL
Anti-GBM antibody seen in:
- Autoimmune glomerulonephritis.
- Goodpasture’s syndrome.
- Tubulointerstitial nephritis.
- Some patients with lupus nephritis.