Wright's Stain, 500x

Howell-Joly bodies in a canine blood smear

Howell-Joly bodies have little clinical significance. There is a tendency to confuse these with Heinz bodies, however. Howell-Joly bodies are remnants of the nucleus (observe the round dark blue structure) in the red blood cell which may persist after the maturation of the erythrocyte and extrusion of the nucleus, and so have nothing to do with the oxidation of hemoglobin which is responsible for the formation of Heinz bodies (which can be observed as a protruberance on the surface of red blood cells). The red blood cells which contain nuclear remnants will be removed from the circulation by the reticuloendothelial system when they pass through the spleen. In cases of regenerative anemia, or reduced or absent splenic function, the number of Howell-Joly bodies in the circulation may increase due to increased erythropoiesis and decreased phagocytic activity, respectively.