Hematology and Hematopoiesis Reading VT122

Hematology

Definition of Hematology

  • Hematology is the science involved with the study of blood cells and their formation.

Role of Veterinary Technician in Hematology Testing

  • Vital for providing accurate and reliable clinical laboratory test results to veterinarians.
  • Understanding principles of hematology tests is essential for accuracy.
  • Recent focus has led to technicians performing more diagnostic testing to enhance animal care and clinic revenue.

Complete Hematology Profile

  • Indicated for:
    • Diagnostic evaluation of disease states.
    • Well-animal screening (e.g., geriatric).
    • Screening tool before surgery.
Complete Blood Count (CBC) Includes:
  1. Red Blood Cell (RBC) Count
  2. White Blood Cell (WBC) Count
  3. Hemoglobin Concentration
  4. Packed Cell Volume (PCV)
  5. Differential White Blood Cell Film Examination
  6. Calculation of Absolute Values
  7. Erythrocyte Indices
Additional Tests
  • Reticulocyte counts
  • Measurement of total solids
  • Thrombocyte (platelet) estimates
Bone Marrow Evaluation
  • Necessary for:
    • Unexplained nonregenerative anemia
    • Leukopenia
    • Thrombocytopenia
    • Pancytopenia (i.e., decreased numbers of all cell lines)
    • Confirmation of infections (e.g., ehrlichiosis) and hematopoietic neoplasms (e.g., lymphoproliferative disorders).

Normal Values and Reference Ranges

  • Found in Appendix B.
  • Affected by:
    • Testing methods
    • Equipment type
    • Patient age, gender, breed, reproductive status

Hematopoiesis

Definition of Hematopoiesis

  • Hematopoiesis refers to the production of blood cells and platelets.

Components of Whole Blood

  • Whole blood is composed of:
    • Plasma (fluid component): Approximately 90% water, 10% dissolved constituents (proteins, carbohydrates, vitamins, hormones, enzymes, lipids, salts, waste)
    • Cellular Component: Includes red blood cells (RBCs or erythrocytes), white blood cells (WBCs or leukocytes), and platelets (thrombocytes).

Types of WBCs

  • Agranulocytes:
    • Lymphocytes
    • Monocytes
  • Granulocytes:
    • Neutrophils
    • Eosinophils
    • Basophils
Blood Cell Lifespan
  • Constantly produced and replaced throughout an animal’s life.
  • Variants exist between juvenile and adult animals.
Sites of Hematopoiesis
  • Prenatal Stage:
    • Liver, spleen, thymus, red bone marrow.
  • Neonatal and Juvenile Stage:
    • Primary site is red bone marrow found in nearly every bone.
  • Adult Stage:
    • Retained mainly in long bones (femur, tibia, humerus, ulna), hips, sternum, ribs.
    • With hematopoietic stress, the liver and spleen can reactivate to produce blood cells.
Blood Cell Production Process
  1. Erythropoiesis: Production of erythrocytes
  2. Leukopoiesis: Production of leukocytes
  3. Thrombopoiesis: Production of platelets
Hematopoietic Stem Cells (HSCs)
  • Pluripotent stem cells can develop into any blood cell type and regenerate.
  • HSCs differentiate into hematopoietic progenitor cells:
    • Common myeloid and lymphoid progenitors.
Major Stimuli (Cytokines)
  • Nearly two dozen cytokines guide the maturation and differentiation of blood cells.

Erythropoiesis

Erythropoietin (EPO)

  • Primary cytokine responsible for RBC production, predominantly produced by kidney cells in response to low blood oxygen.
  • Stimulates red bone marrow erythroid precursor to divide and mature.
Stages of Erythropoiesis
  1. Proerythroblast: develops into rubriblasts.
  2. Rubriblasts: small round nuclei, one or more nucleoli.
  3. Prorubricytes: Slightly smaller with condensed nucleus.
  4. Rubricytes: marked nuclear clumping, hemoglobin synthesis begins.
  5. Metarubricytes: condensed nuclei, no cell division possible.
  6. Reticulocytes: immature RBCs, containing ribosomal material (diffuse blue-gray or polychromatophilic); lose ribosomal material as they mature.

Thrombopoiesis

Thrombopoietin

  • Mainly produced in liver endothelial cells and stimulates megakaryoblast differentiation.
  • Progenitors differentiate through several forms into megakaryocytes that release platelets.
Thrombocyte Formation Process
  • Megakaryocytes shed cytoplasmic fragments into circulation forming platelets (thrombocytes).

Granulopoiesis

Myeloblasts

  • Larger cells with round nuclei; undergo several stages into mature granulocytes (eosinophils, basophils, neutrophils).
Stages in Granulocyte Production
  1. Myeloblasts.
  2. Promyelocytes.
  3. Myelocytes.
  4. Metamyelocytes.
  5. Band cells.
  6. Segmented granulocytes.

Monopoiesis

Development Stages

  1. Monoblast: similar to myeloblasts
  2. Promonocyte and then monocyte.
  • Monocytes transform into macrophages upon specific cytokine exposure.

Lymphopoiesis

Development Process

  • Common lymphoid progenitor produces T cells, B cells, and NK cells.
  • T cells mature in the thymus, B cells generally in bone marrow or GALT, NK cells in lymphoid tissues.

Hematologic Terminology

Definitions

  • -penia: Decreased number of cells.
  • -philia or -cytosis: Increased number of cells.
  • Left shift: Increased immature neutrophils.
  • Leukemia: Neoplastic blood/bone marrow cells.
  • Leukemoid response: Reactive leukocytosis (similar to leukemia).
Collection and Handling of Blood Samples
  1. Determine tests needed; choose appropriate collection vessel.
  2. Preferred source: venous blood.
  3. Common sites for venipuncture include the jugular vein, cephalic vein, etc.
  4. Clean and swab site with alcohol before collection; allow to dry.
  5. Restrain animal to minimize stress during collection.
  6. Blood collection methods:
    • Needle and syringe.
    • Vacuum system (e.g., Vacutainer).

Blood and Plasma Components

Plasma

  • Fluid portion containing water, proteins, hormones, etc.

Serum

  • Plasma without fibrinogen, acquired after clotting occurs.
Anticoagulants
  • Prevent or delay clotting:
    • Heparin: use with caution; not for differential film analysis.
    • EDTA: preferred for hematologic studies.
    • Citrate/Oxalates: used in specific testing.

Sample Volume

  • Affects accuracy of results depending on hydration status of the patient.

Interpretation of CBC

  • Components of CBC:
    • Total RBC count
    • Packed cell volume (PCV)
    • Plasma protein concentration
    • Total WBC count
    • Blood film examination: differential WBC count, morphology.
    • Reticulocyte count
    • Hemoglobin concentration
    • Erythrocyte indices

Assessment of PCV

  • PCV indicates % RBC volume in blood.
  • Measurements done with microhematocrit tubes/capillary tubes.
Normal Values
  • Ranges vary by species listed in Appendix B.
  • Interpretation based on hydration, anemia presence, etc.

Influence on Results

  • Dilute blood, age, animals' stress level can skew interpretations.
  • PCV without proper preparation may yield misleading results.

Interpretation of Hemoglobin Concentration

  • Low levels often indicate anemia.
  • Evaluated along with other test results for disease manifestation.

Summary of Anemia

  • Classification According to Response:
    • Regenerative vs. nonregenerative
  • Classifying by RBC size:
    • Microcytic, macrocytic, normocytic
  • Assess with reticulocyte count, erythrocyte indices, morphology from smears.

Coagulation Factors

  • Understanding hemostasis is required to assess bleeding disorders.

Types of Coagulation Disorders

  1. Primary disorders: inherited factors.
  2. Secondary disorders: trauma, liver disease, etc.
  3. Example: von Willebrand Disease.

Essential Notes on Sample Collection

  • Accurately collect and handle blood to avoid contamination.
  • Essential minimums for species to ensure safe handling and testing.
Conclusion
  • Understanding the above concepts is vital for forming a solid foundation in veterinary hematology, ensuring both accurate diagnostics and the welfare of the animals being treated.

Appendix

  • For more details on normal reference values, please consult Appendix B.