What test determines the number of immature red blood cells?

The test that determines the number of immature red blood cells is called a reticulocyte count. This test measures the percentage of reticulocytes, which are immature red blood cells, in the blood. An elevated reticulocyte count can indicate increased production of red blood cells, often in response to anemia or blood loss. Conversely, a low reticulocyte count may suggest decreased red blood cell production, which can occur in various medical conditions.