The Erythrocyte Count, also known as the RBC Count, is a simple blood test that measures the number of red blood cells (erythrocytes) in a person’s bloodstream. The test is typically ordered as part of a complete blood count (CBC) and is used to evaluate the body’s ability to carry oxygen. The normal range for RBC count varies depending on age, gender, and other factors, but a healthy adult male typically has a range of 4.5-5.5 million cells per microliter (mcL) of blood, while a healthy adult female typically has a range of 4.0-5.0 million cells/mcL. Low RBC counts can be caused by anemia, bleeding, or bone marrow disorders, while high RBC counts can be caused by dehydration, smoking, or certain medical conditions like polycythemia vera.