Overview
This lecture explains key red blood cell (RBC) indices and lab tests used to diagnose and interpret different types of anemia, focusing on iron deficiency anemia and related findings.
RBC Indices & Key Labs
- Hemoglobin and Hematocrit (H&H) measure oxygen-carrying capacity and blood volume percentage of RBCs.
- Mean Corpuscular Volume (MCV) measures average RBC size.
- Mean Corpuscular Hemoglobin (MCH) measures average RBC hemoglobin content.
- Red Cell Distribution Width (RDW) measures variation in RBC sizes; normal is ≤15%.
- Elevated RDW (>15%) means greater size variation among RBCs, often seen in recent-onset anemias.
- Serum iron measures circulating iron levels in blood.
- Serum ferritin measures iron stores in the body.
- Reticulocyte count measures immature RBCs, reflecting bone marrow response to anemia.
- Peripheral smear is a blood test examining RBC shape, size, and color under a microscope.
- Total Iron Binding Capacity (TIBC) measures available iron-binding sites; it increases when serum iron is low due to a reciprocal relationship.
Iron Deficiency Anemia (IDA)
- IDA is characterized by reduced iron, resulting in microcytic (small) and hypochromic (pale) RBCs.
- Most patients are asymptomatic until H&H drops to about 30/10.
- Symptoms include fatigue, dizziness, and worsening of existing diseases, especially in older adults.
- Lab findings: low H&H, low serum iron, low ferritin, decreased MCV and MCH, increased RDW (>15%) in recent onset, increased TIBC.
- In chronic IDA, RDW may normalize (<15%) as all RBCs become uniformly small.
- Peripheral smear helps detect mixed anemias (more than one anemia type present) by showing two RBC populations.
Mixed Anemia & Peripheral Smear Utility
- Mixed anemia means a patient has two types of anemia simultaneously (e.g., iron deficiency and B12 deficiency).
- Peripheral smear is crucial for identifying mixed anemia by revealing both microcytic and macrocytic cells.
Key Terms & Definitions
- RDW — Red Cell Distribution Width, measures RBC size variation.
- MCV — Mean Corpuscular Volume, average size of RBCs.
- MCH — Mean Corpuscular Hemoglobin, average hemoglobin per RBC.
- Serum ferritin — Protein indicating iron stores in the body.
- Reticulocyte — Immature RBC released from bone marrow.
- Peripheral smear — Lab slide of blood to visually assess RBC size and color.
- TIBC — Total Iron Binding Capacity, measures body’s capacity to bind iron.
- Microcytic — Abnormally small RBCs.
- Hypochromic — Abnormally pale RBCs.
- Mixed anemia — Presence of more than one anemia type in a patient.
Action Items / Next Steps
- Review the definitions and functions of RBC indices and lab tests.
- Practice interpreting CBC reports and identifying lab findings consistent with IDA.
- Prepare for upcoming anemia discussions, focusing on microcytic anemias like IDA and thalassemia.