Red blood cells are responsible for transporting oxygen from the lungs to the tissues. They are produced in the bone marrow and have a lifespan of 120 days. Therefore, the bone marrow must continually produce new red blood cells to replace those that have aged and those that have been lost through bleeding. This requires normal bone marrow and adequate quantities of other factors, including iron, folic acid and vitamin B12.
A low number of red blood cells causes anemia. Anemia can be caused by bleeding (trauma, digestive bleeding), the destruction of red blood cells by antibodies or structural defects, hemoglobin abnormalities and enzyme deficiencies. Other causes include iron, folic acid or vitamin B12 deficiency; bone marrow damage (toxins, leukemia); chronic kidney failure; and chronic inflammatory diseases.
A high number of red blood cells (polyglobulia) can be caused by dehydration, chronic lung disease or congenital heart disease. Other causes include smoking, EPO (athletes, kidney tumour), abnormal hemoglobin or bone marrow disruption (true polycythemia).