Haematopoiesis Process and Development

Haematopoiesis

• Haematopoiesis is the process by which all blood cells are formed and develop from hematopoietic stem cells (HSCs).
• Haematopoiesis occurs in different locations in the body depending on the stage of life:
  • Embryo: Yolk sac
  • Fetus: Liver and spleen
  • After Birth and Throughout Life: Primarily occurs in the bone marrow
• In children, haematopoiesis takes place in almost all bones, while in adults, it is confined to the pelvis, vertebrae, sternum, and ribs.

Hematopoietic Tissues or Organs

• These sites are called hematopoietic tissues or organs.
• The bone marrow is the primary site in adults.

Extramedullary Haematopoiesis

• Extramedullary haematopoiesis refers to the production of blood cells outside the bone marrow, such as in the liver and spleen.
• This can occur in response to certain diseases or conditions that impair the marrow's ability to produce blood cells.

Schematic Diagram of Haematopoiesis

• Folate is needed for the synthesis of thymidine, a nucleotide necessary for DNA replication and cell division.
• Vitamin B12 is required for the regeneration of tetrahydrofolate, the active form of folate.
• A deficiency in either vitamin leads to impaired DNA synthesis, resulting in megaloblastic anemia characterized by the presence of large, immature red blood cells.

Red Cell Membrane

• Anemia: A condition characterized by a deficiency in the number or quality of red blood cells, leading to reduced oxygen-carrying capacity of the blood.
• Erythrocytosis: An increase in the number of red blood cells in the blood.
• Polycythaemia: A condition characterized by an increased concentration of hemoglobin in the blood, due either to a reduction in plasma volume or an increase in red cell numbers.

Energy Production in Erythrocytes

• Erythrocytes rely on glycolysis for energy production as they lack mitochondria.
• The glycolytic pathway is used, which consists of two main phases – the preparatory phase and the payoff phase.
• The pentose phosphate pathway (PPP) is also involved.

Enzyme Deficiencies and Their Effects

• Deficiencies in the enzymes of these pathways can lead to hemolytic anemia due to impaired red cell metabolism and membrane stability.
• Hereditary deficiencies include:
  • Pyruvate kinase deficiency
  • Glucose-6-phosphate dehydrogenase (G6PD) deficiency

Glucose-6-Phosphate Dehydrogenase (G6PD)

• Function: Catalyzes the first step in the pentose phosphate pathway, producing NADPH, which protects red cells from oxidative damage.
• Clinical implications of G6PD deficiency:
  • Hemolysis: Oxidative stress from infections, certain foods, or drugs can lead to hemolysis in G6PD-deficient individuals.

Beta Thalassemia

• Severe anemia requiring regular blood transfusions and iron chelation therapy.
• Clinical manifestations include:
  • Severe anemia
  • Growth retardation
  • Skeletal abnormalities
  • Splenomegaly
  • Jaundice
  • Complications of iron overload from transfusions
• Laboratory test features:
  • Hemoglobin electrophoresis (to detect abnormal hemoglobin variants)
  • Complete blood count (CBC) with peripheral smear (to assess RBC morphology)
  • Iron studies (to assess iron overload)
  • Genetic testing for beta thalassemia mutations

Haemoglobinopathies

• Structure of Haemoglobin S:
  • Haemoglobin S (HbS) differs from normal adult hemoglobin (HbA) by a single amino acid substitution where glutamic acid is replaced by valine in the beta globin chain.
• Effect on hemoglobin function:
  • HbS tends to polymerize under conditions of low oxygen tension, causing red blood cells to become rigid and assuming a sickle shape.

Haemolytic Anaemia

• Definition: A condition where red blood cells (RBCs) are destroyed faster than they can be produced.
• Molecular diagnostics:
  • Analyzes genetic material (DNA or RNA) for mutations or rearrangements.
  • Techniques include polymerase chain reaction (PCR), DNA sequencing, and microarray.

Leukaemia

• Definition: Malignant proliferation of hematopoietic stem cells in the bone marrow, leading to abnormal white blood cell production.
• Acute vs. Chronic Leukaemia:
  • Acute leukemia progresses rapidly and requires immediate treatment.
  • Chronic leukemia progresses more slowly.
• Causes of imbalance:
  • Genetic mutations
  • Environmental factors
  • Exposure to carcinogens

Chronic Myeloid Leukaemia (CML)

• Characterized by the Philadelphia chromosome (t(9;22)), leading to the BCR-ABL1 fusion gene.
• Classified into three phases:
  • Chronic
  • Accelerated
  • Blast Crisis
• Classification systems for leukaemia:
  • AML FAB (French-American-British) classification: Based on morphology and cytochemistry.
  • ALL FAB classification: Based on cell lineage and morphology.

Laboratory Testing for Leukaemia

• Includes morphology, flow cytometry, cytogenetics, and molecular testing.
• Morphology: Examination of blood and bone marrow smears.
• Flow cytometry: Identifies cell surface markers.
• Cytogenetics: Detects chromosomal abnormalities.
• Molecular testing: Identifies specific genetic mutations.

Diagnosing Chronic Myeloid Leukemia (CML)

• Clinical presentation: Patients may present with nonspecific symptoms like fatigue, weight loss, or abdominal fullness due to splenomegaly.
• Screening tests:
  • Complete blood count (CBC) with peripheral smear
  • Blood chemistry tests
  • Coagulation studies
• Further testing:
  • Flow cytometry
  • Cytogenetics
  • Molecular testing

Quality Control

• Importance and definition: Quality control ensures the accuracy and reliability of laboratory test results.
• Accuracy and precision:
  • Accuracy refers to how close a measured value is to the true value.
  • Precision refers to the consistency of measured values.
• Levy-Jennings curve: A graphical representation of QC data over time, used to monitor the stability and performance of an assay.
• Calibrator: A substance with a known concentration used to calibrate the assay and ensure accurate measurement of unknown samples.
• QC samples: Monitor the ongoing performance of the assay, ensuring that results fall within acceptable ranges.