Whole Blood and Red Blood Cells
Red Blood Cells (RBCs) are perhaps the most recognizable component of whole blood. RBCs contain hemoglobin, a complex protein containing iron that carries oxygen through the body. The percentage of blood volume composed of red blood cells is called the “hematocrit.” There are about one billion red blood cells in two to three drops of blood, and for every 600 red blood cells, there are about 40 platelets and one white cell.
Manufactured in the bone marrow, RBCs are continuously produced and broken down. They live for about 120 days in the circulatory system. Red blood cells are prepared from whole blood by removing plasma, or the liquid portion of the blood, and they are used to treat anemia while minimizing an increase in blood volume. Improvements in cell preservation solutions over decades have increased the shelf-life of red blood cells from 21 to 42 days.
RBCs may be treated and frozen for an extended storage, of 10 years or more. Patients who benefit most from transfusion of red blood cells include those with chronic anemia resulting from kidney failure or gastrointestinal bleeding, and those with acute blood loss resulting from trauma.
Prestorage leukocyte-reduced red blood cells require special preparation by removing leukocytes (white blood cells) by filtration shortly after donation. This is done before storage because high numbers of leukocytes remaining in a unit of RBCs during the storage process can fragment, deteriorate, and release cytokines (chemicals that affect the inflammatory response). Leukocytes have been implicated as a cause of reactions to a current and subsequent blood transfusions in some transfusion recipients.