Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (534 page)

   Serum C3 and total hemolytic complement activity (CH50) fall during the active disease and return to normal within 6–8 weeks in 80% of cases. If C3 is low for more than 8 weeks, lupus nephritis or MPGN should be considered.

   Serum cholesterol may be increased.

   Renal biopsy shows characteristic findings with EM and immunofluorescence microscopy.

   Chronic renal insufficiency is reported in ≤20% of patients.

GLOMERULONEPHRITIS, RAPIDLY PROGRESSIVE (CRESCENTIC)

   Definition

   Rapidly progressive GN (RPGN) is characterized by progressive loss of renal function and severe oliguria and renal failure that develop over a period of few weeks.

   The histopathologic term “crescentic” refers to crescent formation, a nonspecific response to severe injury to the glomerular capillary wall. Patients may have rapidly progressive GN in association with anti–glomerular membrane (anti-GBM) antibody disease (Goodpasture syndrome), a condition in which circulating antibodies are directed against an antigen in the glomerular basement membrane, resulting in progressive glomerulonephritis and, in approximately 60% of patients, pulmonary hemorrhage. RPGN can also be associated with Wegener granulomatosis, small vessel vasculitis, SLE, or cryoglobulinemia. Depending on the specific disorder, antineutrophil cytoplasmic antibodies (ANCA) can be present in the serum of RPGN patients.

   Who Should Be Suspected?

   Candidates include patients with rapidly developing oliguria or anuria and acute onset of hematuria and edema, especially in the presence of an underlying immunologically mediated systemic illness, or following an infection or administration of certain drugs (e.g., allopurinol, hydralazine, rifampin,
D
-penicillamine).

   Three types of RPGN can be distinguished according to the underlying mechanism of the glomerular injury:

   Type I: mediated by anti-GBM antibodies (<5% of RPGN cases; ≤40 of patients are ANCA positive).

   Type II: mediated by immune complexes (45% of cases; <5% of patients are ANCA positive).