Oxygen–hemoglobin dissociation curve the fluid that surrounds it. Hemoglobin (Hb) is the primary vehicle for transporting oxygen in the blood. Oxygen is also carried dissolved in the blood's plasma, but to a much lesser degree. Hemoglobin is contained in red blood cells. Under certain conditions, oxygen bound to the hemoglobin is released into the blood's plasma and absorbed into the tissues. Each hemoglobin molecule has the capacity to carry four oxygen molecules. These molecules of oxygen bind to the iron of the Heme group. The binding of the first oxygen molecule induces a conformational change of hemoglobin that increases the affinity for the
Red blood cell be used for blood transfusions. Several blood tests involve red blood cells. These include a "RBC count" (the number of red blood cells per volume of blood), calculation of the hematocrit (percentage of blood volume occupied by red blood cells), and the erythrocyte sedimentation rate. The blood type needs to be determined to prepare for a blood transfusion or an organ transplantation. Many diseases involving red blood cells are diagnosed with a blood film (or peripheral blood smear), where a thin layer of blood is smeared on a microscope slide. This may reveal abnormalities of red blood cell shape and