PAE510 — Diseases of the Blood: Lecture Note

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la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: PAE 510 Course title: Diseases of the Blood Course credit load: 2 Units Series 1: The Haematopoietic System and Evaluation of Anaemia in Children • Part 1.1: The Haematopoietic System: Definition, Components, and Development o Sub Part 1.1.1: Definition and components of the haematopoietic system o Sub Part 1.1.2: The bone marrow and haematopoiesis o Sub Part 1.1.3: Development of the haematopoietic system • Part 1.2: Evaluation of a Child with Haematologic Disorders o Sub Part 1.2.1: General principles of evaluating a child with a suspected haematologic disorder o Sub Part 1.2.2: Key elements of history in suspected haematologic disorders o Sub Part 1.2.3: Physical examination in suspected haematologic disorders • Part 1.3: General Approach to Anaemia: History, Examination, and Laboratory Evaluation o Sub Part 1.3.1: Definition of anaemia and relevant patient characteristics o Sub Part 1.3.2: History and physical examination in anaemia o Sub Part 1.3.3: Laboratory evaluation of anaemia • Part 1.4: Classification of Anaemia o Sub Part 1.4.1: Classification of anaemia by red cell size o Sub Part 1.4.2: Normocytic anaemia and reticulocyte response o Sub Part 1.4.3: Confirmatory testing Introduction Picture a pale, tired eight year old brought to clinic by a concerned mother, with a full blood count returning a low haemoglobin, prompting the essential next question of exactly what type of anaemia this represents and why. Understanding the haematopoietic system and developing a structured, systematic approach to evaluating a child with anaemia forms the essential foundation

la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS for this entire PAE 510 course, since the specific diseases of the blood discussed in later Series all ultimately present, at least in part, through their effects on this same system. The aim of this Series is to equip you with an understanding of the haematopoietic system and its development, and a structured approach to evaluating a child with haematologic disorders, particularly anaemia. This Series begins with the definition, components, and development of the haematopoietic system, before turning to the evaluation of a child with haematologic disorders. Next, we examine the general approach to anaemia, including history, examination, and laboratory evaluation, before concluding with the classification of anaemia. Series Learning Outcomes At the end of this Series, you should be able to: • SLO 1.1: define the haematopoietic system and describe its components, • SLO 1.2: describe the development of the haematopoietic system, • SLO 1.3: describe the evaluation of a child with haematologic disorders, • SLO 1.4: define anaemia and describe relevant patient characteristics, including age, sex, race, and ethnicity, • SLO 1.5: describe the history and physical examination relevant to a child with anaemia, • SLO 1.6: describe the laboratory evaluation of anaemia, including full blood count, RBC indices, blood smear, and reticulocyte count, • SLO 1.7: describe the classification of anaemia by red cell size, and • SLO 1.8: describe confirmatory testing in the evaluation of anaemia, including haemoglobin electrophoresis. 1.1 The Haematopoietic System: Definition, Components, and Development 1.1.1 definition and components of the haematopoietic system A system responsible for producing every blood cell The haematopoietic system, abbreviated HS, refers to the collective organs and tissues responsible for the production, maturation, and regulation of blood cells, and comprises three principal components: the blood cells themselves, the bone marrow, the primary site of blood cell production, or haematopoiesis, in postnatal life, and the lymphoid organs, including the

la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS spleen, lymph nodes, and thymus, which support lymphocyte development and immune function. Blood cells are broadly classified into three main lineages: red blood cells, or erythrocytes, responsible for oxygen transport, white blood cells, or leukocytes, responsible for immune defence, further subdivided into granulocytes, lymphocytes, and monocytes, and platelets, responsible for haemostasis, and all three lineages ultimately arise from a common haematopoietic stem cell population within the bone marrow. Fill in the blank: The haematopoietic system comprises blood cells, the bone marrow, and ________ organs. 1.1.2 the bone marrow and haematopoiesis The bone marrow contains haematopoietic stem cells, capable of both self-renewal and differentiation into all the mature blood cell lineages, through a carefully regulated process involving specific growth factors and cytokines, such as erythropoietin, stimulating red cell production, and various colony-stimulating factors, stimulating white cell production, each acting on specific progenitor cell populations at different stages of maturation. In children, active bone marrow, capable of producing blood cells, is distributed more widely throughout the skeleton than in adults, in whom active marrow becomes progressively confined to the axial skeleton and proximal long bones with increasing age, a normal developmental change with practical relevance to the interpretation of bone marrow biopsy findings and imaging at different ages. Fill in the blank: Erythropoietin is a growth factor that stimulates ________ cell production. 1.1.3 development of the haematopoietic system Haematopoiesis during fetal development occurs sequentially in different anatomical sites, beginning in the yolk sac in very early gestation, transitioning to the liver and spleen during mid-gestation, and finally to the bone marrow, which becomes the dominant site of haematopoiesis by late gestation and remains so throughout postnatal life, a sequential pattern reflecting the changing anatomical and physiological requirements of the developing fetus. Understanding this normal developmental sequence has practical clinical relevance, since extramedullary haematopoiesis, the resumption of blood cell production in the liver or spleen outside the bone marrow, can occur postnatally in certain pathological states where bone marrow function is significantly compromised or overwhelmed, effectively representing a reversion to this earlier, fetal pattern of blood cell production.

la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: Extramedullary haematopoiesis is the resumption of blood cell production outside the ________ marrow. Figure 1.1: The lineages of blood cell development from a common haematopoietic stem cell. Pilot questions 1.1 1. Define the haematopoietic system and list its three principal components. (Linked to SLO 1.1) 2. List the three main lineages of blood cells and their general function. (Linked to SLO 1.1) 3. Describe the role of erythropoietin and colony-stimulating factors in haematopoiesis. (Linked to SLO 1.1) 4. Describe the sequential sites of haematopoiesis during fetal development. (Linked to SLO 1.2) 5. Define extramedullary haematopoiesis and explain when it can occur postnatally. (Linked to SLO 1.2)

la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.2 Evaluation of a Child with Haematologic Disorders 1.2.1 general principles of evaluating a child with a suspected haematologic disorder A structured approach across history, examination, and testing Evaluation of a child with a suspected haematologic disorder requires a structured approach combining a detailed history, thorough physical examination, and appropriately selected laboratory investigations, since haematologic disorders can present with a genuinely wide range of clinical features, from entirely asymptomatic laboratory abnormalities identified incidentally, to significant, even life-threatening, acute presentations requiring urgent evaluation and management. The specific pattern of presentation, together with relevant patient characteristics, discussed further in the next Part of this Series, meaningfully narrows the likely differential diagnosis before any laboratory testing is even performed, meaning careful, structured clinical assessment remains genuinely central to efficient, accurate evaluation rather than relying on laboratory testing alone to reach a diagnosis. Fill in the blank: The specific pattern of presentation, together with relevant patient characteristics, meaningfully narrows the likely differential ________. 1.2.2 key elements of history in suspected haematologic disorders A focused history should establish the presenting symptoms, such as fatigue, pallor, bruising, or bleeding, together with their onset, duration, and progression, and relevant background history, including family history of haematologic conditions, dietary history, particularly relevant to nutritional causes of anaemia, discussed further later in this Series, and any history of chronic illness or medication use that might contribute to a haematologic abnormality. Birth history and developmental history are also relevant, particularly in younger children, given the potential for certain congenital or inherited haematologic conditions, discussed in detail in later Series of this course, to present from early infancy, and a thorough, systematic history genuinely helps distinguish between the many possible underlying causes of a given haematologic presentation before examination and testing even begin. Fill in the blank: A focused history should establish presenting symptoms such as fatigue, pallor, bruising, or ________.

la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.2.3 physical examination in suspected haematologic disorders Physical examination should include careful assessment for pallor, best assessed at the conjunctivae, palms, and nail beds, jaundice, suggesting possible haemolysis, lymphadenopathy and hepatosplenomegaly, which may suggest an underlying malignant or infiltrative process, and bruising or petechiae, suggesting a possible underlying bleeding disorder, discussed in detail in the final Series of this course. Growth parameters should also be assessed, given the potential for chronic haematologic disease to affect growth, and a thorough, systematic examination, considering the whole child rather than focusing narrowly on a single presenting feature, remains essential, since haematologic

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