Clinical Hematology Overview

Clinical Hematology Lecture Notes

• Hematology is the study of blood cellular elements (red blood cells, white blood cells, and platelets) and how those blood components are used to diagnose and monitor disease.
• Pluripotent hematopoietic stem cells divide slowly, maintaining their own population, and differentiate into myeloid and lymphoid stem cells.
• Myeloid lineage precursors (blasts) encompass erythrocytes, thrombocytes, granulocytes, and monocytes, all developed in the bone marrow.
• Lymphoid lineage cells include B and T lymphocytes, and natural killer cells; their development occurs in lymphoid tissues.
• Erythrocytes (red blood cells) lack nuclei and are packed with hemoglobin for oxygen transport. They are biconcave discs for increased surface area and efficient gas exchange.
• Three routine measurements for red blood cells (RBCs) are packed cell volume (PCV), hemoglobin concentration, and RBC count. These measurements are related and can be used to calculate Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin Concentration (MCHC).
• Anemia is a clinical state of low red blood cell mass and a significant finding in hematological disorders, defined as a reduction in red blood cell mass.
• Anemia can be due to blood loss (acute or chronic), hypoproliferation, or hemolysis.
• Erythropoiesis (red blood cell production) is regulated by erythropoietin, which is produced in the kidneys in response to low blood oxygen levels.
• Anemia can be categorized into various types based on morphology and causes, including microcytic, normocytic, and macrocytic anemias.
• Evaluating the reticulocyte count, MCV, and RDW are helpful for diagnosing and differentiating anemia causes. A low reticulocyte count (<75,000/μL) suggests a hypoproliferative cause, while a high reticulocyte count (>100,000/μL) suggests hemolysis or a rapid response to blood loss.
• A peripheral blood smear provides critical visual information about blood cells. Anomalies like hypersegmented neutrophils can indicate megaloblastic processes.
• Bone marrow aspiration and biopsy are important when there's diagnostic uncertainty regarding hypoproliferative anemia; evaluation of cellular morphology and bone marrow architecture is crucial. This procedure can identify various hematological disorders such as myelodysplasia, leukemia, lymphoma, and myeloma.

Products and Functions of Blood Cells

• Erythrocytes' primary product is hemoglobin, responsible for oxygen transport.
• Leukocytes (WBCs) possess various granules with different functions; neutrophils phagocytose bacteria, eosinophils target parasitic helminths, basophils release inflammatory mediators, monocytes generate macrophage cells, lymphocytes produce antibodies (B cells), and NK cells kill infected or cancerous cells.
• Platelets produce clotting factors to stop bleeding.

Classification of Blood

• Whole blood consists of plasma and formed elements.
• Plasma is the liquid component containing various substances like amino acids, nutrients, proteins (albumins and globulins), fibrinogen, electrolytes, and gases.
• Formed elements include erythrocytes, leukocytes (granulocytes and agranulocytes), and platelets.

Systemic Approach to Anemia

• A thorough history and physical examination, along with a complete blood count (CBC), concentrating on MCV and RDW, plus reticulocyte count, are crucial for anemia diagnosis; these parameters help classify anemia types and narrow down causes.

History and Physical Examination for Anemia

• Fatigue is a common but unspecific symptom.
• History of systemic illnesses, diabetes mellitus, medications, occupational exposures (e.g., lead), social history including drug use, and dietary habits are important elements to analyze in patients with anemia.

More Specific Findings

• Signs like angular cheilitis, koilonychia, splenomegaly, or cardiac murmurs may accompany an underlying anemia.
• These findings can help narrow down the potential causes of anemia. If present in children they may suggest a congenital cause.

Examination of the Peripheral Blood Smear

• A peripheral blood smear remains a valuable tool for confirming blood cell count results, diagnosing underlying health conditions, and confirming differential diagnosis suspected during initial tests. Visual examination can assist in identification of blood dyscrasias and other blood cell abnormalities

Bone Marrow Examination

• Bone marrow aspiration and biopsy evaluate cellular morphology and architecture of the bone marrow; they can be used to confirm and classify hematological disorders by visual inspection.
• Bone marrow examinations are useful for diagnosing hematological disorders like dysplasia, leukemia, and lymphoma.
• Findings might include abnormalities in maturing red blood cells, or abnormalities in other lineages.
• Anomalies may suggest malignancies or infiltrative disease processes affecting bone marrow.