What percentage of whole blood do red blood cells constitute by volume?

• A. Less than 1%
• B. About 45%
• C. About 54.3%
• D. About 0.7%

Answer: (B)

Red blood cells, or erythrocytes, typically make up about 45% of whole blood by volume in a healthy adult. This percentage can vary slightly depending on factors such as hydration levels, altitude, and individual health conditions, but it generally hovers around this value.

The reason this percentage is significant is due to the primary function of red blood cells, which is to transport oxygen from the lungs to the tissues and return carbon dioxide from the tissues back to the lungs. They contain hemoglobin, a protein that binds to oxygen, and their relative abundance in blood plays a crucial role in maintaining effective oxygen delivery throughout the body.

In clinical settings, this percentage is also used to assess various health conditions. For example, a significantly lower percentage might indicate anemia, whereas a higher percentage might suggest conditions like polycythemia. The values provided in the incorrect options illustrate values that do not accurately reflect the typical hematocrit (the volume percentage of red blood cells in blood), helping to further clarify the relevance of the correct answer.