Reticulocyte

A reticulocyte is an immature erythrocyte (i.e., red blood cell), which are primarily present in bone marrow but may circulate in blood. When reticulocytes circulate in a higher than normal percentage of erythrocytes, it suggests that erythropoiesis is being hyperactive. When the reticulocyte percentage is zero to low in the presence of anemia, it suggests depressed erthryopoiesis.

The name comes from a microscopic staining technique by which they were first characterized, in which parts of the ribosomes collect in a "reticulated" pattern. This collection is not the same as the endoplastic reticulum.