Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

Which test is used to determine the number of immature RBC?

1. Osmotic fragility test

2. Reticulocyte count

3. RBC count

4. Stab cell count

The correct answer is: Reticulocyte count

The reticulocyte count is specifically designed to measure the number of immature red blood cells (RBCs) in the bloodstream. Reticulocytes are newly formed RBCs that still contain some of their cell organelles, which gives them a characteristic appearance when stained and viewed under a microscope. This test is significant in assessing bone marrow function and the body’s response to anemia or blood loss, as an elevated reticulocyte count indicates that the bone marrow is producing more RBCs in response to low hemoglobin levels. The osmotic fragility test assesses the ability of red blood cells to withstand varying concentrations of saline, primarily used to evaluate conditions like hereditary spherocytosis. The RBC count measures the total number of red blood cells, without distinguishing between mature and immature cells. The stab cell count, which is less commonly referred to in clinical practice, relates to the assessment of nucleated red blood cells in certain pathological states but does not specifically target the count of immature RBCs like reticulocytes do. Thus, the reticulocyte count effectively indicates the turnover rate of erythropoiesis, making it the most relevant choice for determining the number of immature RBCs.