Anti-GBM antibody

Sample

1. This test is done on the venous blood to get the serum.
2. The patient needs to fast for 8 hours.
3. Another sample is a tissue biopsy of the kidney (lung tissue).

Purpose of the test (Indications) for Anti-GBM antibody

1. To diagnose autoimmune-induced glomerulonephritis.
2. To differentiate from the other type of glomerulonephritis.
3. To diagnose Goodpasture’s syndrome.

Precaution for Anti-GBM antibody

• Drugs like antibiotics may decrease the test result.

Pathophysiology of Anti-GBM glomerulonephritis

1. This is an autoimmune phenomenon.
   1. About 5% of glomerulonephritis is Anti-GBM type.
   2. Some autoantibodies react with the basement membrane of the renal glomeruli capillaries.
      1. These autoantibodies react with small blood vessels of the kidney and lung.
      2. These autoantibodies react with pulmonary alveoli.
   3. When these antibodies react only with the glomeruli basement, they give rise to anti-GBM glomerulonephritis.
   4. In Goodpastaur syndrome, there are circulating antibodies against the glomerular basement membrane. These antibodies also react against the alveoli of the lung.

2. The mechanism of the tissue damage is a type III hypersensitivity reaction where immune complexes activate the complement system.
   1. Immune complexes give rise to:
      1. Glomerulonephritis leads to hematuria.
      2. Pulmonary hemorrhage leads to hemoptysis.
      3. Positive autoantibodies against basement membranes.

Anti-GBM type III reaction

3. This hypersensitivity reaction is complement-mediated.
   1. The damage is due to the deposition of immune complexes.

Goodpasture’s syndrome:

1. It is an autoimmune disease and characterized by:
2. 1. When both kidney and lung are involved.
   2. Hematuria.
   3. Hemoptysis (pulmonary hemorrhage).
   4. Antibodies to the basement membrane, which acts as an antigen.
3. 60% to 70 % of the cases, both kidney and lung are involved (Goodpasture’s syndrome).
   1. 20% to 40 % of the cases show only involvement of the kidneys only then called anti-GBM glomerulonephritis.
4. When there is the involvement of the lung, the patient will have blood in a cough.

Diagnosis of Anti-GBM glomerulonephritis and Goodpasture syndrome:

1. The serum method is easy, faster, and more reliable in patients with a difficult or contraindicated biopsy.
   1. Blood by enzyme immunoassay (EIA):
   2. Negative = <20 units
   3. Borderline  = 20 to 100 units
   4. Positive = >100 units
2. The high anti-GBM titer is suggestive of :
   1. Goodpasture’s syndrome.
   2. Lupus erythematosus.
   3. Anti-GBM nephritis.
3. Lung or renal biopsy demonstrates these antibodies by immunohistochemical technique.

Normal anti-GMB antibody

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
• A negative result does not rule out Goodpasture’s syndrome.

Anti-GBM antibody seen in:

1. Autoimmune glomerulonephritis.
2. Goodpasture’s syndrome.
3. Tubulointerstitial nephritis.
4. Some patients with lupus nephritis.

Questions and answers: