Identification of intrarenal fibrin deposition

The site and extent of intrarenal fibrin deposition has been examined by routine histological staining, immunofluorescence, and electron microscopy in 109 patients with a wide variety of renal diseases. The findings have been correlated with the amount of urinary fibrin/fibrinogen degradation product (FDP) excretion as measured by the tanned red cell haemagglutination inhibition immunoassay. The results show that routine histological stains (Martius Scarlet Blue and Picro Mallory) are unreliable, particularly where there is mesangial accumulation of material or where the amount of fibrin deposited is small and confined to a subendothelial position. Similarly the electron microscope may overassess the degree of fibrin deposition, particularly if this is associated with the deposition of immunoglobulins and complement. There is a close relationship between the site and extent of fibrin, as detected by immunofluorescence, and the maximal urinary FDP excretion.