Red blood cell thus much more common than the other blood particles: there are about 4,000–11,000 white blood cells and about 150,000–400,000 platelets per microliter. Human red blood cells take on average 60 seconds to complete one cycle of circulation. The blood's red color is due to the spectral properties of the hemic iron ions in hemoglobin. Each human red blood cell contains approximately 270 million of these hemoglobin molecules. Each hemoglobin molecule carries four heme groups; hemoglobin constitutes about a third of the total cell volume. Hemoglobin is responsible for the transport of more than 98% of the oxygen in the body
Red blood cell form. When red blood cells sometimes occur as a stack, flat side next to flat side. This is known as "rouleaux formation", and it occurs more often if the levels of certain serum proteins are elevated, as for instance during inflammation. Red blood cells can be obtained from whole blood by centrifugation, which separates the cells from the blood plasma in a process known as blood fractionation. Packed red blood cells, which are made in this way from whole blood with the plasma removed, are used in transfusion medicine. During plasma donation, the red blood cells are pumped back into