Basic Hematology Principles and RBC Indices

Basic Hematology Principles

• Whole blood comprises erythrocytes, leukocytes, platelets, and plasma.
• The buffy coat contains leukocytes and platelets.
• Serum is the liquid part of clotted blood, lacking fibrinogen. Both serum and plasma are about 90% water.
• Formed elements vary in size: thrombocytes (2-4 µm), erythrocytes (6-8 µm), lymphocytes (6-9 µm), reactive lymphocytes (10-22 µm), basophils (10-15 µm), segmented neutrophils (10-15 µm), band neutrophils (10-15 µm), eosinophils (12-16 µm), and monocytes (12-20 µm).

RBC Indices

• Mean Corpuscular Volume (MCV): Indicator of average RBC volume; normal value: 80-100 fL; Normocytic (80-100 fL), Microcytic (<80 fL). Increased in megaloblastic anemia, hemolytic anemia, liver disease, and normal newborns; decreased in iron deficiency, thalassemia, sideroblastic anemia, and lead poisoning.
• Mean Corpuscular Hemoglobin (MCH): Indicator of average hemoglobin weight in individual RBCs; normal value: 26-34 pg.
• Mean Corpuscular Hemoglobin Concentration (MCHC): Measure of average hemoglobin concentration; normal value: 32-37 g/dL; Hypochromic ( <32 g/dL), seen in iron deficiency and thalassemia; 38 g/dL suggests spherocytes; >38 g/dL indicates a machine error.
• Anisocytosis: Increased variation in RBC size.
• Anisochromia: Variation in RBC color.
• RBC Distribution Width (RDW): Normal value: 11.5-14.5%; reflects anisocytosis; elevated in post-transfusion states, post-treatment, idiopathic sideroblastic anemia, and dual deficiencies (iron and folate).
• Hematocrit: Percentage of RBCs in whole blood; normal values: Males 41-53%, Females 36-46%. Microhematocrit is the reference manual method.
• Hemoglobin: Normal values: Males 13.5-17.5 g/dL, Females 12.0-16.0 g/dL.
• Platelets: Normal value: 150-450 x 10⁹/L or 150,000-450,000/µL.
• Mean Platelet Volume (MPV): Normal value: 6.8-10.2 fL.

Hematology Staining

• Romanowsky stains (nonvital): Wright's stain (most common), uses methanol as fixative, eosin (acidic), methylene blue (basic), and phosphate buffer (pH 6.4-6.8).
• Prussian blue (nonvital monochrome): Visualizes iron granules; contains potassium ferrocyanide, HCl, and a safranin counterstain.
• Supravital stains (living cells): New methylene blue or brilliant cresyl blue (for reticulocytes); neutral red with brilliant cresyl green (for Heinz bodies). No fixative needed.

Hematopoiesis

• Continuous regulated process of blood cell formation (renewal, proliferation, differentiation, maturation).
• Occurs in the reticuloendothelial system (RES): bone marrow, spleen, liver, thymus, and lymph nodes.
• Bone marrow: Primary site by 24 weeks gestation; red marrow is hematopoietically active; yellow marrow is inactive (adipocytes).
• Retrogression: Transformation of red marrow to yellow marrow.
• Cellularity: Ratio of marrow cells to fat; normocellular (30-70% hematopoietic cells), hypercellular (>70%), hypocellular (<30%).

Test your knowledge on the essential principles of hematology, including blood components and RBC indices. This quiz covers concepts related to erythrocytes, leukocytes, platelets, and their respective measurements. Understand how to interpret the Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin (MCH).