Hematuria of tubular origin

Hematuria (HU) of tubular origin is described on the basis of ultrastructural investigations of two rejected human renal allografts. The red blood cells (RBC) got into the interstitium through the walls of the damaged intertubular capillaries, and, via ruptures of the tubular basement membrane (BM), they may pass from the interstitium into the tubular lumen, causing HU. Rupture of the tubular BM may develop owing to the enzymes released by interstitial inflammatory cells or to the difference in the interstitial and intratubular pressures. Some of the RBC already in the tubular lumen may penetrate between the epithelial cells and even between the epithelium and the BM, probably because of the locally increased intraluminal pressure. If the RBC reach the BM, the epithelial cells produce a new, thin BM above them, with disintegration of the outer older one, and, thus, the RBC may pass into the interstitium again. This phenomenon is called the tubulointerstitialis circulation of RBC.