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Diseases of Platelet Number: Immune Thrombocytopenia, Neonatal Alloimmune Thrombocytopenia, and Posttransfusion Purpura

Platelets are anucleate cells that are required for primary hemostasis. A normal platelet count is 150,000 to 400,000 platelets per microliter of blood, with a normal lifespan of 7 to 10 days for circulating platelets. The body clears 10 11 platelets per day by balancing complex proapoptotic and antiapoptotic mechanisms. Exogenous reagents and environmental changes can also impact the rate of platelet clearance by the cells…

Acquired Disorders of Platelet Function

Acquired disorders of platelet function are among the most common hematologic abnormalities, which reflects the sensitivity of platelets to external and internal perturbations. The clinical challenge in evaluating acquired disorders of platelet function is to determine whether observed derangements in platelet function pose a threat to the patient. Although altered platelet function can predispose patients to either hemostatic or thrombotic disorders, this chapter deals primarily, but…

Laboratory Evaluation of Hemostatic and Thrombotic Disorders

This chapter provides a practical approach to the laboratory evaluation of hemostatic and thrombotic disorders. Any assessment of hemostatic or thrombotic disorders must start with a thorough history and physical examination. These can provide clues to guide subsequent laboratory testing, diagnosis, and management. Physiologic hemostasis is a complex interplay of cellular or plasma elements: the adhesion of platelets to damaged endothelium, the aggregation of platelets to…

Evaluation of the Patient With Suspected Bleeding Disorders

Bruising and bleeding are common reasons for a hematology referral. Some consults are for management of an acute bleed in someone who may have a hemorrhagic disorder. Such bleeds may be spontaneous or occur after surgery or trauma, and the potential bleeding disorder may be inherited or acquired. With acute bleeding problems, the approach to patients must be rapid and directed at urgent restoration of hemostasis.…

Molecular Basis of Blood Coagulation

Blood is the principal vehicle delivering oxygen and nutrients to the various tissues and organs of the body. Blood flow and the integrity of the vasculature are essential to life itself. The hemostatic process has evolved to provide damage recognition and protection from blood loss after perforation of the vasculature while at the same time preventing the systemic activation of the clotting system. However, pathologic occlusions…

Molecular Basis of Platelet Function

A primary physiological role of platelets is to support hemostasis at sites of vascular injury by forming a plug that arrests blood loss ( Fig. 124.1 ). Normally, disc-shaped platelets circulate in the bloodstream without adhering to the endothelium of the vessel wall. When the endothelium is damaged, platelets adhere to the exposed subendothelial collagen and, at high shear, to collagen-immobilized von Willebrand factor (VWF). Platelet…

Megakaryocyte And Platelet Structure

Platelets are small anucleate fragments that are formed from the cytoplasm of megakaryocytes and have a characteristic discoid shape. To assemble and release platelets, megakaryocytes become polyploid by endomitosis and follow a maturation program that results in the conversion of the bulk of their cytoplasm into multiple long processes called proplatelets . To produce its quota of 1000 to 2000 platelets, a megakaryocyte may release as…

Blood Vessels

Hemostatic, Hematopoietic, and Vascular Systems as a Functional Continuum Diseases affecting the bone marrow (BM) and peripheral blood are closely intertwined with the state of the vascular system, which acts as a niche, conduit, and regulator of blood cells. This is exemplified by the anatomic proximity and interactions among several related cellular populations, including hematopoietic stem and progenitor cells and their mature progeny, endothelial cells, perivascular…

Overview of Hemostasis and Thrombosis

Introduction Hemostasis preserves vascular integrity by balancing the physiologic processes that maintain blood in a fluid state under normal circumstances and prevent excessive bleeding after vascular injury. Preservation of blood fluidity depends on an intact vascular endothelium, and a complex series of regulatory pathways that maintain platelets in a quiescent state and keep the coagulation system in check. In contrast, arrest of bleeding requires rapid formation…

Transfusion and Apheresis Support for Sickle Cell Disease Patients

Transfusion of red cells in all patients is primarily triggered by the need to increase oxygen delivery to tissues in the setting of blood loss or anemia. For patients with sickle cell disease (SCD), there are additional considerations for transfusion including the need to remove sickle hemoglobin (HbS) containing cells in specific clinical settings. These settings include acute complications (e.g., acute chest syndrome) of SCD or…

Pediatric Transfusion Medicine

A variety of neonatal and pediatric patients require blood component transfusions. This chapter focuses on aspects of blood-bank laboratory testing, blood products and components, transfusion indications, and potential adverse events that are specifically relevant to neonates and children. Pediatric Blood Banking Blood and Blood Components Several different blood components, including whole blood, reconstituted whole blood, red blood cells (RBCs), platelets, plasma, and cryoprecipitated antihemophilic factor (CRYO)…

Transfusion-Transmitted Diseases

Adverse reactions following blood transfusion reflect immunologic, pathophysiologic, and microbiologic events. This chapter presents information about transfusion-associated viral, bacterial, parasitic, and prion infections and discusses a number of emerging agents including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Transfusion-transmitted infection risk mitigation through blood donor screening and blood testing strategies are presented. The boxed discussions provide insights into interventions aimed at reducing risk from known and…

Transfusion Reactions to Blood and Hematopoietic Stem Cell Therapy Products

A transfusion reaction can be defined broadly as any adverse event that occurs in association with the infusion of a blood or cell therapy product. Transfusion reactions are classified by how close to transfusion they occur (timing), how much morbidity is caused (severity), how strong the causal association of the event is with transfusion (imputability), as well as by its fit to a (standardized) definition of…

Hemapheresis

Therapeutic bloodletting is an ancient therapy that dates back to the Galenic conceptualization of illness caused by the imbalance of the four humors. The practice remained fashionable, albeit unproved, well into the 19th century. About the time that scientific skepticism began to temper the widespread use of therapeutic phlebotomy, a new technique for blood removal, apheresis, appeared in the research laboratory. The term apheresis , derived…

Principles Of Plasma And Plasma Derivatives

Plasma and its derivatives are well-established clinical resources, but cost, risk of infectious disease transmission, although rare, and other adverse effects mandate their appropriate use. Even to this day, however, much still remains to be clarified regarding the appropriate clinical indications/protocols for plasma product use. Plasma can be separated from red blood cells (RBCs) through centrifugation of whole blood at the time of collection or can…

Human Leukocyte Antigen and Human Neutrophil Antigen Systems

This chapter reviews human leukocyte antigen (HLA) and human neutrophil antigen (HNA) systems. A general background of the structure, function, and nomenclature of both systems and their relevance in clinical hematology is presented. Analysis of HLA gene products is applied in clinical settings (1) to select compatible donor-recipient pairs for transplantation, (2) to select HLA-compatible single-donor platelet products for thrombocytopenic patients refractory to standard transfusion of…

Clinical Considerations in Platelet Transfusion Therapy

Platelet Collection and Manufacturing Platelet components are either prepared from whole blood donations (platelet concentrates) or are collected by apheresis (single donor platelets). In the United States, whole blood–derived platelet concentrates are produced using the platelet-rich plasma (PRP) method. First, a whole blood unit is separated by gentle centrifugation (slow spin) into red blood cells (RBCs) and PRP. The PRP is then centrifuged a second time…

Principles of Red Blood Cell Transfusion

The clinical practice of transfusion medicine has evolved substantially since the discovery of the ABO system around 1900. Two technological advances set the stage for clinical practice through blood component therapy. First, the introduction of a safe and effective anticoagulant-preservative solution (suggested by Loutit and Mollison) allowed for the preservation of blood products. Second, in the mid-1960s, the introduction of plastic blood bags by Walter and…

Human Blood Group Antigens and Antibodies

Pretransfusion testing includes ABO and Rhesus (Rh) type, and antibody screening to determine whether a patient has an unexpected red blood cell (RBC) antibody. If the antibody screen is positive, an identification panel is performed to identify the specificity. Unexpected antibodies can be clinically significant causing hemolysis (i.e., acute or delayed hemolytic reaction) after transfusion of RBCs carrying the reciprocal antigen, or can be insignificant. The…

Supportive Care for the Transplant Patient

Although hematopoietic cell transplantation (HCT) is a therapeutic option for various hematological and non-hematological disorders, it can result in toxicities and complications, leading to significant treatment related morbidity and non-relapse mortality (NRM). Based on the temporal association from the date of HCT, these may be divided into early complications (within the first 3 months of HCT) or late complications (beyond 3 months of HCT), but can…