In evaluating anemia, what is the most important initial parameter to determine the cell size category?

• A. Checking WBC count
• B. Assessing MCV to classify anemia
• C. Measuring reticulocyte count
• D. Evaluating iron saturation

Answer: (B)

Determining the red blood cell size starts with the MCV, the mean corpuscular volume. This parameter directly measures how large or small the average red cell is and classifies anemia as microcytic, normocytic, or macrocytic (rough ranges: microcytic <80 fL, normocytic 80–100 fL, macrocytic >100 fL). That classification guides the likely causes and next steps in workup. The other tests don’t specify cell size: white blood cell count isn’t about red cell morphology; reticulocyte count shows marrow response or production rate rather than size; iron saturation reflects iron availability but not the actual size category of red cells. So using MCV first to categorize the anemia by cell size is the most informative initial step.