Whole blood is composed of 4 primary components: red blood cells (RBCs), white blood cells (WBCs), platelets, and plasma.
Red blood cells
Most people associate blood with RBCs. And perhaps rightly so—they are the component in greatest demand for transfusions. RBCs contain hemoglobin, which enables cells to deliver oxygen throughout the body and gives blood its red color. Because of the high demand for RBCs, critical shortages are common.
White blood cells
WBCs play an important role in the human immune system. They protect the body against bacteria, viruses, and other pathogens that cause illness.
Platelets
Platelets are small, disk-shaped blood components. They are critically important to the blood clotting process. Platelets stick together, or coagulate, along the lining of blood vessels. Without them, we would not survive the common, everyday blood vessel leakage that can occur in any of us.
Plasma
Plasma is the liquid portion of blood. (It’s 90% water!) It contains RBCs, WBCs, and platelets. Not only does plasma help maintain satisfactory blood pressure and body fluid volume, it also provides proteins that fight infections and diseases, and promotes proper clotting.