Which of the following urine sediment components is associated with glomerulonephritis?

RBC casts are associated with glomerulonephritis due to the nature of the condition itself, which involves inflammation and damage to the glomeruli—tiny filtration units in the kidneys. When the glomeruli are compromised, they become more permeable, allowing red blood cells (RBCs) to escape from the capillaries into the urine. These RBCs can then aggregate and form casts, which are cylindrical structures made up of proteins and cells that take the shape of the renal tubules.

In the context of glomerulonephritis, the presence of RBC casts is indicative of glomerular bleeding. They suggest that the bleeding is coming from within the nephron rather than after the kidney, which would typically result in free RBCs in the urine instead of casts. Therefore, observing RBC casts in urine sediment is a significant diagnostic marker for glomerulonephritis and highlights a pathological process occurring within the glomeruli.