What is GBM (glomerular basement membrane)?
A membrane which is part of kidney that helps in filtering waste & extra fluid from blood. It is a specialized extracellular matrix which lies between podocytes (epithelial cells covering outer surface of glomerular capillaries) & endothelial cells (single cell layer lining all blood vessels) of kidney. Together these three layered structures of endothelium, GBM & podocyte help facilitate flow of water & small solutes and restrict large plasma proteins.
What is Anti-GBM lab test?
Hence, anti-GBM are antibodies produced against glomerular basement membrane. They attack part of kidney and are associated with kidney damage. Anti-GBM antibodies attack capillaries in GBM which causes problems in kidney function. Hence, as a result blood and blood proteins leak into urine. Sometimes, anti-GBM antibodies can also attack lung basement membrane which causes lung damage and difficulty breathing. This laboratory test detects anti-GBM antibodies in blood.
Why is Anti-GBM lab test done?
The test helps in diagnosing diseases which affect kidneys and lungs; hence, it is done:
- Evaluation in patients with rapid onset of renal (kidney) failure (it comes under anti-GBM glomerulonephritis as only kidneys get affected)
- Pulmonary (lung) hemorrhage
- Aids in diagnosis of Goodpasture syndrome i.e. glomerulonephritis with rapid onset renal failure & pulmonary hemorrhage both occur.
Reference range for all ages is:
- <1.0 U: Negative; you have none of the anti-GBM antibodies present in blood.
- > or = 1.0 U: Positive; indicates that anti-GBM antibodies are present and points towards two possibilities i.e. either you have anti-GBM disease or Goodpasture syndrome. However, most of the time the positive results are consistent with Goodpasture’s syndrome (highly specific).
This test is used to diagnose certain kidney diseases, such as Goodpasture syndrome and anti-glomerular basement membrane disease.
