Unit
- Erythrocytes (red blood cells): These are the most numerous cells in the blood, responsible for oxygen transport via hemoglobin. A healthy adult has approximately 4.5-5.5 million red cells per microliter. Their biconcave shape increases surface area for gas exchange, and they lack nuclei to maximize hemoglobin capacity.
- Leukocytes (white blood cells): These cells form the immune system's cellular defense. They are classified into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes). Each type has distinct roles in combating infection, from phagocytosis to antibody production.
- Thrombocytes (platelets): Small, disc-shaped cell fragments derived from megakaryocytes in the bone marrow. Their primary function is hemostasis: adhering to damaged endothelium, aggregating, and releasing factors that initiate coagulation. Normal count ranges from 150,000 to 450,000 per microliter.
- Plasma: The liquid component of blood, comprising about 55% of total volume. It contains water, electrolytes, proteins (albumin, globulins, fibrinogen), nutrients, hormones, and waste products. Plasma serves as the transport medium for all blood cells and dissolved substances.
- Complete blood count (CBC): This is the foundational diagnostic test in hematology. It provides quantitative information about each cell line: red cell indices (MCV, MCH, MCHC), white cell differential, and platelet count. Automated analyzers now also report flags for abnormal cells.
- Peripheral blood smear: A manual examination of a stained blood film under a microscope. This allows qualitative assessment of cell morphology, including size, shape, and inclusion bodies. It remains essential for confirming automated results and detecting subtle abnormalities.
- Blood cell life span and turnover: Red cells survive about 120 days, platelets 7-10 days, and some white cells only hours. The bone marrow produces approximately 200 billion red cells daily to maintain homeostasis. Understanding turnover helps interpret laboratory values and disease states.
- Clinical significance of cell proportions: The normal hematocrit (packed cell volume) is about 40-50% in men and 36-46% in women. Deviation indicates anemia or polycythemia. The white cell differential shows relative percentages; a shift to the left indicates increased immature neutrophils seen in infection.
- Hemoglobin structure and variants: Hemoglobin is a tetramer of globin chains and heme groups. Adult hemoglobin (HbA) contains two alpha and two beta chains. Variants such as HbS (sickle cell), HbC, and HbE result from point mutations. These alter oxygen affinity and stability, leading to various anemias and diagnostic patterns on electrophoresis.
- Coagulation cascade overview: The coagulation system comprises intrinsic, extrinsic, and common pathways culminating in fibrin clot formation. Key factors include fibrinogen, prothrombin, and tissue factor. Laboratory tests such as PT, aPTT, and fibrinogen levels assess each pathway. Deficiencies cause bleeding disorders like hemophilia or vitamin K deficiency.
- Bone marrow examination: Bone marrow aspiration and biopsy evaluate hematopoietic tissue. Aspiration provides cells for morphology and flow cytometry; biopsy reveals cellularity and architecture. Indications include unexplained cytopenias, suspected leukemia, or staging of lymphomas. The procedure is performed by a physician with local anesthesia.
Scope of Practice
Role: Hematology Laboratory Technician
Within scope:
- Preparing and staining peripheral blood smears according to standard protocol
- Operating automated hematology analyzers and performing daily quality control checks
- Identifying and reporting abnormal cell morphology to the pathologist
- Performing manual differential counts and reticulocyte counts
- Maintaining records of all test results and instrument maintenance
Outside scope:
- Interpreting clinical significance of results for patient management
- Diagnosing hematologic disorders or recommending treatment
- Informing patients of test results or prognosis
- Modifying testing protocols without supervisor approval
- Performing bone marrow aspiration or biopsy procedures
Quick Revision
- Blood consists of erythrocytes, leukocytes, thrombocytes, and plasma, each with specific functions.
- Complete blood count and peripheral blood smear are key diagnostic tools in hematology.
- Cell life spans vary: red cells 120 days, platelets 7-10 days, white cells hours to days.
- Hematology laboratory technicians perform technical testing but do not diagnose or treat patients.