Reticulocytopenia, or "aplastic crisis", is the medical term for an abnormal decrease of reticulocytes in the body. Reticulocytopenia can originate from congenital hemolytic anemia

Hemolytic anemia

Hemolytic anemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells , either in the blood vessels or elsewhere in the human body . It has numerous possible causes, ranging from relatively harmless to life-threatening...

, especially when exacerbated by Parvovirus B19

Parvovirus B19

The B19 virus, generally referred to as parvovirus B19 or sometimes erythrovirus B19, was the first known human virus in the family of parvoviruses, genus erythrovirus...

 infection. Can occur with Sickle Cell Anemia and Spherocytosis

Spherocytosis

Spherocytosis is an auto-hemolytic anemia characterized by the production of red blood cells , or erythrocytes, that are sphere-shaped, rather than bi-concave disk shaped. Spherocytes are found in hereditary spherocytosis and autoimmune hemolytic anemia.It almost always refers to hereditary...

, where hemoglobin levels fall rapidly and the marrow cannot compensate, causing absence of reticulocytes. Reticulocytes are immature red blood cells.