73  Basics

Published

September 6, 2025

73.1 Introduction

Pediatric haematology requires an understanding of how the blood and blood-forming organs develop anatomically, how they function physiologically, and how disease processes disrupt these systems. Children differ significantly from adults in their hematologic profiles due to developmental changes, increased metabolic demands, and perinatal transitions. In Ghana and Sub-Saharan Africa, the clinical spectrum is strongly influenced by infectious diseases (malaria, HIV, TB), nutritional deficiencies, and inherited disorders such as sickle cell disease (SCD).

This chapter provides an integrated review of anatomy, physiology, and pathology of the hematopoietic system, with emphasis on conditions most relevant to children in the region.

73.2 Anatomy of the Hematologic System

The hematologic system includes the bone marrow, blood cells, lymphoid organs, the reticuloendothelial system, vascular endothelium, and plasma proteins.

73.2.1 Bone marrow

  • Sites of hematopoiesis
    • Fetal life: yolk sac → liver & spleen → bone marrow (by third trimester).
    • Postnatal: whole skeleton initially; becomes restricted to the axial skeleton (sternum, ribs, pelvis, vertebrae) during adolescence.
  • Cellularity
    • Neonates and infants: very high cellularity (~80–90%); gradually becomes fattier with age.
  • Components
    • Hematopoietic stem cells (HSCs), stromal cells (fibroblasts, adipocytes), sinusoids, and supporting extracellular matrix.

Clinical relevance: High marrow activity in infants enables robust erythropoiesis but also means bone marrow failure syndromes present early and dramatically. Bone marrow aspiration is essential when leukaemia or aplasia is suspected.

73.2.2 Lymphoid organs

  • Thymus
    • Large and active in childhood; required for T-cell maturation.
    • Involution begins in adolescence.
    • Absent or underdeveloped thymus → severe T-cell deficiency (e.g., DiGeorge syndrome).
  • Spleen
    • Filters aged/damaged RBCs; participates in immune responses and can host extramedullary hematopoiesis.
    • Vulnerable to sequestration in SCD; frequently enlarged in malaria-endemic settings.
  • Lymph nodes
    • More reactive and often enlarged in children due to frequent antigen exposure.

73.3 Physiology of the Hematologic System

73.3.1 Hematopoiesis

Definition: production of blood cells from multipotent HSCs.

Developmental stages

  1. Yolk sac hematopoiesis (early gestation)
  2. Foetal liver (mid to late gestation) — primary site until birth
  3. Bone marrow (dominant after birth)

Paediatric differences

  • Infants have higher baseline erythropoietic activity.
  • Lymphopoiesis is intensified during early childhood for immune maturation.

73.3.2 Red blood cell physiology

  • Haemoglobin switching: HbF (α₂γ₂) predominates at birth (≈70–80%). Switch to HbA (α₂β₂) occurs over the first 6 months.
  • Physiologic anaemia of infancy: Postnatal fall in erythropoietin causes a nadir in haemoglobin at ~6–8 weeks; usually mild and self-limiting.
  • Oxygen affinity: HbF has higher O₂ affinity than HbA — clinically significant for newborn adaptation.

Clinical links

  • Hemoglobinopathies (e.g., SCD) typically become clinically significant after HbF declines.

  • Nutritional deficiencies (iron, folate, B12) rapidly impair RBC production due to high turnover.

73.3.3 White blood cell physiology

  • WBC composition: Infants often have relative lymphocytosis; neutrophil counts are lower in early life than in older children and adults.
  • Immune maturation: Neonates and young infants have immature innate and adaptive immune responses.

Clinical links

  • Distinguish physiologic lymphocytosis from pathologic causes (e.g., lymphoid leukaemia).

  • Severe neutropenia increases the risk of fulminant bacterial infections.

73.3.4 Platelet and coagulation physiology

  • Platelet counts in neonates are broadly similar to those of adults.
  • Neonatal factor levels: Lower vitamin K stores and reduced levels of some vitamin K-dependent clotting factors (II, VII, IX, X) increase bleeding risk.
  • Vitamin K prophylaxis at birth is crucial to prevent Vitamin K Deficiency Bleeding (VKDB).

73.4 Pathology in Pediatric Haematology

Hematologic pathology in children can be classified by the affected cell line or process: production, maturation, destruction, and hemostasis.

73.4.1 Disorders of red blood cells

73.4.1.1 Anaemia (physiologic classification)

  • Production failure: iron deficiency, folate/B12 deficiency, bone marrow failure (aplastic anaemia).
  • Destruction (hemolysis): sickle cell disease, G6PD deficiency, malaria-related hemolysis, and immune hemolytic anaemia.
  • Blood loss: trauma, gastrointestinal blood loss (e.g., hookworm), peripartum haemorrhage.

Local epidemiology (Ghana & region):

  • Severe anaemia in children <5 commonly results from malaria + iron deficiency.

  • Sickle cell disease is a major contributor to hemolytic anaemia and childhood morbidity.

73.4.1.2 Hemoglobinopathies

  • Sickle cell disease (HbSS): vaso-occlusive crises, acute chest syndrome, splenic sequestration, stroke risk.
  • Thalassemias: less frequent in West Africa than in the Mediterranean/SE Asia, but should be considered in microcytic anaemia unresponsive to iron.

73.4.1.3 Polycythemia

  • Neonatal polycythemia from delayed cord clamping, maternal diabetes, or twin-twin transfusion syndrome.

73.4.2 Disorders of white blood cells

  • Neutropenia: viral causes, drug-induced (e.g., chloramphenicol), congenital forms.
  • Leukocytosis & blasts: often reactive, but a high blast percentage suggests leukaemia (ALL is the most common childhood leukaemia).
  • Immunodeficiencies: primary (SCID, DiGeorge) and secondary (malnutrition, HIV).

73.4.3 Platelet and coagulation disorders

  • Thrombocytopenia: ITP (post-infectious), dengue (epidemic settings), marrow infiltration (leukaemia).
  • Coagulation defects: haemophilia A/B, von Willebrand disease, VKDB, and DIC (seen in severe sepsis and complicated malaria).

73.4.4 Reticuloendothelial and lymphoid pathology

  • Splenomegaly: chronic malaria, SCD (early enlargement; later autosplenectomy), portal hypertension, malignancy.
  • Lymphadenopathy: reactive infections, TB lymphadenitis, lymphomas.

73.5 4 Integrating Anatomy, Physiology and Pathology — Clinical Perspectives

Component Normal (Anatomy/Physiology) Pathology Pediatric/Local Relevance
Bone marrow High cellularity in infancy Aplastic anaemia, leukaemia Early pancytopenia is often dramatic
HbF → HbA switch HbF is dominant at birth SCD symptoms as HbF falls Hydroxyurea raises HbF and reduces crises
Thymus Central to T-cell maturation Thymic aplasia → SCID Recurrent severe infections in infancy
Spleen Filters RBCs, immune role Sequestration, autosplenectomy Major role in SCD & malaria pathology
Vitamin K stores Low in neonates VKDB Important in out-of-facility births
Immune maturation Lymphocyte predominance early Leukocyte disorders Distinguish physiologic vs pathologic counts

73.6 Practical Approach to Common Presentations

73.6.1 Child with pallor / suspected anaemia

  1. History: onset, feeding, bleeding, family history (hemoglobinopathies), recent infections, drug exposure.
  2. Examination: pallor distribution, jaundice, splenomegaly, and signs of heart failure.
  3. Initial investigations:
    • Complete blood count (FBC) with indices
    • Reticulocyte count
    • Peripheral blood film (morphology; malaria parasites on thick/thin films)
    • Malaria RDT where microscopy is unavailable
    • Ferritin/iron studies, if available
    • G6PD assay if hemolysis is suspected
  4. Management principles:
    • Treat underlying cause (e.g., antimalarials, iron for deficiency).
    • Transfusion for severe or symptomatic anaemia (local transfusion guidelines).

73.6.2 Child with bleeding/bruising

  1. Obtain platelet count, PT/INR, and aPTT.
  2. Consider ITP, haemophilia, vWD, and DIC.
  3. Manage bleeding (local measures, tranexamic acid where indicated) and refer for factor assays or specialist care.

73.6.3 5.3 Suspected leukaemia

  1. Red flags: persistent fever, bone pain, bruising, hepatosplenomegaly, abnormal white cell differential with blasts.
  2. Urgent FBC, blood film and prompt referral to a paediatric oncology unit for bone marrow aspirate and staging.

73.7 Management Principles

  • Supportive care: hydration, treating infections, nutritional rehabilitation, and pain control.
  • Transfusion therapy: indicated for severe symptomatic anaemia, acute blood loss, or SCD complications (exchange transfusion for stroke/ACS).
  • Disease-specific therapies: iron replacement, hydroxyurea for SCD, factor replacement for haemophilia, chemotherapy for malignancies.
  • Prevention: newborn screening for SCD, universal vitamin K prophylaxis, routine immunisations, insecticide-treated nets and malaria chemoprophylaxis where indicated, and routine deworming.

73.8 Summary

A working knowledge of the anatomy (bone marrow, thymus, spleen), physiology (developmental hematopoiesis, haemoglobin switching, immune maturation), and pathology (anaemia, hemoglobinopathies, leukaemias, bleeding disorders) is essential for pediatric practice. In Ghana and across Sub-Saharan Africa, high-burden diseases such as malaria, SCD, and nutritional deficiencies shape clinical priorities. Effective care depends on early recognition, appropriate investigation (FBC, blood film, reticulocyte count, coagulation studies), timely supportive measures, and referral for specialised therapies.

73.9 Further reading

  1. Kliegman RM, Stanton B, St. Geme JW III, Schor NF, Behrman RE. Nelson Textbook of Paediatrics.
  2. Hoffbrand AV, Moss PAH. Essential Haematology.
  3. World Health Organisation. Sickle Cell Disease: A Strategy for the WHO African Region.
  4. Ghana Health Service / Ministry of Health – Standard Treatment Guidelines.