This test is used to detect paroxysmal nocturnal hemoglobinuria (PNH) clones by evaluating the expression of CD59, a glycosylphosphatidylinositol (GPI)-anchored protein, on blood cells. Loss or deficiency of CD59 on red blood cells, granulocytes, or monocytes is characteristic of PNH and helps in diagnosis, classification, and monitoring of the disease.