Chapter 28: Assessment of Hematologic Function

Blood consists of fluid plasma (about 55 percent of volume, containing essential proteins like albumin and clotting factors) and cellular elements (40 to 45 percent of volume, including erythrocytes, leukocytes, and platelets). Hematopoiesis, the continuous process of blood cell formation, occurs primarily in the bone marrow, where primitive stem cells differentiate into myeloid lineages (giving rise to red blood cells, platelets, and most white blood cells) or lymphoid lineages (producing T and B lymphocytes and natural killer (NK) cells). Red blood cells (RBCs) transport oxygen via hemoglobin and are produced through erythropoiesis, a process stimulated by erythropoietin released primarily from the kidney in response to diminished oxygen levels. Normal RBC production requires adequate intake of iron, vitamin B12, and folate. Leukocytes, or white blood cells (WBCs), protect the body against infection; subtypes include neutrophils (the primary defense mechanism via phagocytosis, identified by a shift to the left when immature forms like band cells are prevalent), monocytes (which mature into macrophages in tissues), and lymphocytes (key to adaptive immunity, involving T cells for cellular immunity and B cells for humoral immunity/antibody production). Platelets (thrombocytes), which are granular fragments of megakaryocytes, are crucial for coagulation. Maintaining hemostasis requires an intricate balance between clot formation (primary hemostasis involves platelet plug formation; secondary hemostasis involves the coagulation cascade via intrinsic and extrinsic pathways leading to stabilizing fibrin formation) and fibrinolysis (clot dissolution by plasmin). The nursing assessment of hematologic function emphasizes a thorough health history, physical examination, and interpretation of key laboratory diagnostics such as the complete blood count (CBC), coagulation tests (INR, aPTT), and invasive procedures like bone marrow aspiration and biopsy. Therapeutic modalities discussed include surgical splenectomy (often to remove a site of excessive cell destruction), hematopoietic stem cell transplantation (HSCT) for certain disorders, therapeutic apheresis (removing specific components like platelets or plasma), and therapeutic phlebotomy for managing elevated hematocrits or iron overload. A major focus is blood component therapy, requiring meticulous pretransfusion assessment, patient consent, and detailed administration procedures. Potential transfusion complications range from the common febrile nonhemolytic reactions and allergic responses to the life-threatening acute hemolytic reactions (often due to clerical errors), transfusion-related acute lung injury (TRALI), bacterial contamination, and transfusion-associated circulatory overload (TACO). Finally, pharmacologic alternatives, such as hematopoietic growth factors like erythropoietin and granulocyte colony-stimulating factor (G-CSF), are available to stimulate the body's own cell production and thereby reduce the need for blood component transfusions.