Reticulocyte (RTC, Reticulocyte Index, Reticulocyte Percent, Reticulocyte Production Index, RPI)
Reticulocytes are immature red blood cells, typically composing about 1% of the red cells in the human body. Reticulocytes develop in the bone marrow. They circulate in the blood stream for about a day before developing into mature red blood cells. A reticulocyte count is an important indicator of the bone marrow’s recovery properties.
The body maintains about the same red blood cell numbers. A red blood cell lives for approximately 120 days. Old red blood cells are destroyed in the spleen, while new ones develop in the bone marrow. This process is controlled by erythropoietin, a hormone produced in the kidneys. When oxygen levels in the blood fall, the kidneys begin to produce erythropoietin. It is delivered to the bone marrow by the blood causing an increased production of red blood cells. When the required red blood cell levels are reached, the production of erythropoietin in the kidneys is reduced.
The diagnosis of anemia and evaluation of the efficiency of anemia treatment are two main indications for measuring a reticulocyte count in the blood.
An increased reticulocyte count may be indicative of the increased blood formation in the bone marrow caused by either a severe blood loss or effective anemia treatment.
A reticulocyte count may be slightly higher than normal during pregnancy. A low reticulocyte count or lack of reticulocytes is a bad prognostic marker for persons suffering from anemia indicating the suppression of the bone marrow function in charge of red blood cell regeneration.