Red blood cell casts contain intact and disintegrated or crenated red blood cells. When many cells are enclosed within the matrix of the cast, a red blood cell cast appears yellow or reddish-brown. The presence of RBC casts in the urine indicates bleeding into the nephron.
For a cast to be considered a red blood cell cast, the outlines of the red blood cells must be visible in at least one area of the cast.
The image on the right is a RBC cast (400× magnification) viewed using brightfield microscopy.
