The reticulocyte production index (RPI) is a kind of blood test used to diagnose anemia. In the case of anemia, a patient’s red blood cells are depleted, thereby increasing the reticulocyte count. Reticulocytes refer to the red blood cells that are newly produced. This test is usually done as a follow up to the CBC test. A patient is asked to undergo RPI in case he suffers from symptoms like fatigue, paleness, chronic blood loss after trauma, disorders of bone marrow, bone marrow transplant, kidney and liver disorders, medication and chemotherapy.