Which laboratory test determines the number of erythrocytes in a blood sample?

• A. White Blood Cells
• B. Hemoglobin
• C. Red Blood Cells (Erythrocytes) RBC
• D. Platelets

Answer: (C)

The number of erythrocytes is determined by the red blood cell count, which is reported as cells per microliter of blood. This measurement is part of a complete blood count and directly quantifies how many erythrocytes are present. Hemoglobin tells you how much hemoglobin is carried by the blood, hematocrit indicates the proportion of blood volume made up by red cells, and platelets measure the number of platelets. Because RBC count specifically counts the red blood cells themselves, it’s the test that determines the number of erythrocytes.