AANTI-GLOMERULAR BASEMENT MEMBRANE

CLINICAL UTILITY:

A number of patients with nephritis are found to have antibodies to a glycoprotein, which has been shown to be localized to the M2 subunit of the globular domain of collagen IV. The term 'Goodpastures Syndrome' was originally introduced to describe a clinico-pathological entity characterized by lung hemorrhage combined with rapidly progressive oliguric glomerulonephritis. This condition usually results in severe necrosis of the glomerulus with fibrin deposition. Since other causes may also produce the syndrome as described by Goodpasture, anti-glomerular basement membrane (GBM) antibody nephritis is not synonymous with Goodpastures Syndrome, although the terms are sometimes used interchangeably.

Diagnosis of anti-basement membrane antibody disease is based on the immunofluorescent detection of classic linear deposits of IgG, and less frequently IgA or IgM, along the basement membrane. The diagnosis should be confirmed by either elution study or detection of circulating anti-GBM antibodies, since nonimmunologic linear accumulations of IgG and other serum proteins are sometimes identified in kidneys from patients with diabetes mellitus, kidneys obtained at autopsy or following perfusion prior to transplantation and from relatively normal kidneys of patients who are unsuspected of the disease. A few patients with SLE have had evidence of circulating anti-GBM antibodies in addition to numerous other autoantibodies.

It is now apparent that antibodies directed against the GBM cross react with lung basement membrane. This may explain the common association in this syndrome of glomerulonephritis with lung hemorrhage. About 2/3 of patients present with combined renal and pulmonary symptomatology. About 1/3 have glomerulonephritis alone and the remaining 1-2% have their disease confined to the lung.

A flu-like illness is present at the onset in most but not all patients. The glomerular nephritis associated with anti-GBM antibodies is usually severe and rapidly progressive; however, milder and sometimes self-remitting forms of nephritis are being encountered. In patients with Goodpastures Syndrome, nearly 70% are males. However, with glomerulonephritis alone the distribution is more nearly equal. The majority of patients develop the disease during the second or third decades of life. However, the disease has been reported below 10 years and over 70. A second grouping of patients in their 50 and 60's is becoming evident, particularly among females.

Goodpastures Syndrome can be a fatal disease if left untreated. Plasma exchange and immunosuppression have lowered the risk. However, the most important factor for successful treatment seems to be early diagnosis before tissue damage has progressed too far.

METHOD DESCRIPTION:

The method used here to detect anti-glomerular basement membrane (GBM) is an enzyme immunoassay (EIA).

REFERENCE RANGE:

0-20 EU/ml=Negative; 21-50 EU/mL= Indeterminate; >50 EU/mL= Positive

SPECIMEN REQUIREMENTS:

0.5 ml serum (red top tube). Separated from cells and refrigerated or frozen within 8 hours. The samples may be stored at 2-8°C if testing is to be performed within 2 days. If stored longer, the sample should be frozen at -20°C or lower.