Sanne de Bruin

10 Chapter 1 Blood components Blood consists of a cellular and a fluid component. More than 99% of the cells in blood are RBCs. Furthermore, blood contains platelets, and white blood cells. White blood cells, although sometimes used as a transfusion product (i.e. granulocyte transfusions) are beyond the scope of this thesis and therefore will not be discussed any further in this introduction. Plasma is the liquid component of blood andmakes up approximately 55% of the blood volume. It contains numerous proteins, including several coagulation factors. The key function of RBCs is oxygen (O 2 ) and carbon dioxide (CO 2 ) exchange between lungs and peripheral tissues. RBC production, erythropoiesis, is located in the bone marrow. During the process of proliferation and maturation, RBCs lose their nucleus, mitochondria andmost other cell organelles to optimize oxygen binding to haemoglobin (Hb). Under normal physiological circumstances RBCs have a lifespan of circa 120 days and are removed by the red pulp in the spleen and the liver. Anaemia is defined as a low number of circulating RBCs. TheWorld Health Organisation (WHO) defined anaemia in non-pregnant women as Hb level < 12 g/dL and in men < 13 g/dL. Anaemia can have different causes: a decreased erythropoiesis, increased destruction of RBCs and/or loss of RBCs due to bleeding. Treatment includes iron supplementation, administration of erythropoiesis stimulating agents (ESAs) or RBC transfusion and is determined by the severity and the cause of the anaemia. Platelets and coagulation factors in plasma play together with RBCs an essential role in haemostasis. To establish efficient coagulation, platelets and coagulation factors in the plasma are both required. Platelets are cell fragments derived from megakary- ocytes, that lack a nucleus, but contain other cell organelles including mitochondria. The lifespan of platelets in vivo is approximately ten to twelve days. The main function of platelets is to form together with RBCs a blood clot after vessel injury. But platelets also play an important role in several immunological processes 14 . Coagulation factors are proteins, which are mostly produced by the liver. Multiple coagulations factors are described. The half-life differs per factor and ranges between 4 and 300 hours. The coagulation system is activated in response to endothelial damage (Figure 1). During primary haemostasis a platelet and RBC plug forms at the site of the vessel injury. Simultaneously the secondary haemostasis, also known as the coagulation cas- cade, takes place. The coagulation cascade starts with release of tissue factor (extrinsic pathway) or the release of collagen (intrinsic pathway). In the end, in both pathways factor X is produced, which converts prothrombin to active thrombin. Thrombin con-