If RBCs become swollen in dilute urine to the point that the cell membrane ruptures, the cell loses its hemoglobin, leaving only the membrane and free hemoglobin. These empty membranes are known as "ghost" cells.
Phase-contrast microscopy enhances the appearance of the red cell membrane on ghost cells. The cell would be counted as an RBC if the membrane can be visualized. A positive blood result on the reagent dipstick would also help confirm them as RBCs.