What does the presence of dysmorphic RBCs in urine suggest?

The presence of dysmorphic red blood cells (RBCs) in urine strongly suggests glomerular bleeding. Dysmorphic RBCs, which exhibit abnormal shapes due to passage through the glomeruli, indicate that the source of the bleeding is from the kidneys, particularly the glomeruli. The glomeruli are the filtration units of the kidneys, and damage at this level can lead to alterations in the morphology of the RBCs before they are excreted in the urine.

When RBCs are damaged as they pass through the glomerular capillaries, they can become fragmented or take on irregular shapes, known as dysmorphic. In contrast, RBCs that bleed from lower urinary tract sources, such as infections or trauma, tend to appear normal in shape, since they do not undergo the same mechanical stress that causes dysmorphism. Therefore, the identification of dysmorphic RBCs is a key indicator of glomerular pathology, making it a crucial finding in differentiating types of hematuria in clinical practice. This means that the correct interpretation aligns with conditions such as glomerulonephritis or other glomerular diseases, where the integrity of the glomerular filtration barrier is compromised.