The red blood cell (RBC) count is a measure of the number of red blood cells (erythrocytes) per cubic millimeter (mm3) or liter (L) of blood. RBCs, which have a lifespan of 80 to 120 days, are produced by the bone marrow.
The main function of the red blood cell (RBC or erythrocyte) is to carry oxygen from the lungs to the body tissues and to transfer carbon dioxide from the tissues to the lungs. This process is achieved by means of the Hb in the RBCs, which combines easily with oxygen and carbon dioxide and gives arterial blood a bright red appearance. To enable use of the maximal amount of Hb, the RBC is shaped like a biconcave disk—this affords more surface area for the Hb to combine with oxygen. The cell is also able to change its shape when necessary to allow for passage through the smaller capillaries.
RBC production is stimulated by erythropoietin, a hormone secreted by the kidney. The amount of erythropoietin secreted increases whenever tissue hypoxia occurs. Such hypoxia occurs in individuals living at high altitudes or in people who smoke. The result is the production of an increased number of red blood cells, a condition known as polycythemia. If the number of RBCs is decreased below normal, the condition is known as anemia. There are several different types of anemia, with additional testing needed to differentiate among the various types.
Increased in: Cardiovascular disease, Chronic hypoxia, Chronic lung disease, Congenital heart defects, Cushing’s disease, Hemoconcentration, Hepatic cancer, High altitude, Polycythemia vera, Smoking
Decreased in: Addison’s disease, Alcohol abuse, Anemias, Bone marrow suppression, Chronic infection, Chronic renal failure, Hemodilution, Hemolysis, Hemorrhage, Hodgkin’s disease, Hypothyroidism, Leukemia, Multiple myeloma, Myelodysplasia, Rheumatic fever, Subacute bacterial endocarditis, Systemic lupus erythematosus, Vitamin deficiency (B6 , B12 , folic acid).