Reticulocytes are immature RBCs without a nucleus. They retain a fine network of endoplasmic reticulum that stains with reticulocyte stains. These immature cells are slightly larger than mature RBCs and normally circulate in small numbers. Elevated numbers of circulating reticulocytes (reticulocytosis) occur in chronic hemorrhagic or hemolytic anemia with increased erythropoiesis. A lack of circulating reticulocytes in chronic anemia indicates bone marrow depression. Reticulocytosis without evidence of anemia may indicate reduced oxygenation of blood. This leads to increased erythropoietin levels, which in turn stimulate erythropoiesis and release of reticulocytes from the bone marrow. Reticulocytes are not counted by the VetScan HMT but are suggested by a high MCV. When present they indicate the animal is responding to blood loss by red cell regeneration.

An immature red blood cell.

the last immature stage of RBC; they do not carry oxygen as a mature RBC does.

Newly differentiated erythrocytes which contain fine thread-like strands (network) of RNA (ribonucleic acids). The RNA strands may be demonstrated by supravital staining with methylene blue.