Which test counts the number of red blood cells in a sample?

• A. Pulmonary Angiography
• B. Sigmoidoscopy
• C. Red Blood Cells (Erythrocytes) RBC
• D. Thoracentesis

Answer: (C)

Determining the number of red blood cells is about measuring how many erythrocytes are circulating in a given volume of blood, which is captured by the RBC count as part of a complete blood count. This measurement helps assess oxygen-carrying capacity and diagnose conditions like anemia or polycythemia. The test that quantifies erythrocyte numbers directly is the RBC count.

In contrast, pulmonary angiography is an imaging study of the lung blood vessels, sigmoidoscopy inspects the sigmoid colon, and thoracentesis involves removing pleural fluid with a needle. None of these assess the actual number of red blood cells. So the option describing Red Blood Cells (Erythrocytes) RBC is the correct choice.