Howell-Jolly bodies are round, smooth, almost pyknotic, dark-purple bodies ranging in size from 0.5 to 1.0 micron in diameter. These RBC inclusions contain DNA. Howell-Jolly bodies are thought to be nuclear remnants or aggregates of chromosomes that have separated from the mitotic spindle and remain behind after the remainder of the RBC nucleus is expelled. The spleen normally removes these bodies from the RBCs; however, Howell-Jolly bodies can be observed on a Wright-stained peripheral blood smear post-splenectomy or when the spleen is not functioning properly. Howell-Jolly bodies may also be seen in hemolytic anemias such as sickle cell anemia.
When Howell-Jolly bodies are present, they usually occur singly, as shown in the image on the right. It is possible, though, that two or more may be seen in a single RBC, usually occurring in the presence of megaloblastic anemia or abnormal erythropoiesis.