Reticulocytes/Erythrocytes

A red blood cell (RBC) count measures the number of red blood cells, also known as erythrocytes, in your blood. Red blood cells are made in your bone marrow, the spongy tissue inside your large bones. They contain hemoglobin, an iron-rich protein that carries oxygen from your lungs to every cell in your body.

A red blood cell (RBC) count is almost always part of a complete blood count (CBC), a group of tests that measures the number and type of cells in your blood. The RBC measurement is used to help diagnose red blood cell disorders, such as anemia, a condition in which your body does not make enough healthy red blood cells.