The red blood cells of a patient with sickle cell disease have 40% abnormal hemoglobin beta chains that form hemoglobin S (HbS), inherited from one or both parents, thus owning two of them. alleles and a total hemoglobin of 80 to 100%. A carrier of this genetic disease would have an HbS and HbA allele. Under conditions of decreased oxygen, the red blood cells of the SCD individual resemble a sickle or half-moon shape, causing them to stick to each other, thereby blocking blood flow in the vessels, causing pain in the affected joints. This is known as a “vaso-occlusive event (VOE)” (p. 870) and results in increased heart rate, reduced pulse rate, hypotension, and decreased capillary refill. VOE also causes a reduction in the oxygen capacity of hemoglobin reaching tissues and other parts of the body, leading to ischemia. In severe cases and with repeated ischemia, body organs such as the spleen, liver, heart, kidneys, brain, joints, bones, and retina gradually decline in activity and function. (Ignatavicius and Workman,