Anemia is a term used to describe a deficiency in the red blood cell count. Blood is a fluid composed of cells (red cells, white cells, and platelets) and serum (clear fluid). Red and white blood cells are produced in the bone marrow. Red blood cells, which contain hemoglobin, are required to carry oxygen in the body. In a situation where the number of red blood cells is low, the body will be forced to operate under the stress of inadequate oxygen delivery. Some compensation is possible, but only as long as a critical number of red blood cells remains.