Which is the normal reference range for red blood cells (RBC) in adults?

Which is the normal reference range for red blood cells (RBC) in adults?

• A. 4.0-5.0
• B. 4.5-5.5
• C. 4.0-6.0
• D. 3.5-5.5

Answer: (B)

Normal RBC count reflects healthy production in the bone marrow and adequate oxygen-carrying capacity of the blood. For adults, the reference range most commonly used is about 4.5 to 5.5 million red blood cells per microliter of blood. Some laboratories report in SI units as roughly 4.2 to 5.4 x10^12/L, and there are small sex differences: males tend to have slightly higher counts than females due to testosterone and iron loss with menstruation. The 4.5–5.5 range neatly covers typical adult values in many clinical resources, making it the best benchmark. Values below this range can indicate anemia, while values above may suggest polycythemia or dehydration; interpretation should also consider factors like altitude, smoking, or chronic lung disease.

Normal RBC count reflects healthy production in the bone marrow and adequate oxygen-carrying capacity of the blood. For adults, the reference range most commonly used is about 4.5 to 5.5 million red blood cells per microliter of blood. Some laboratories report in SI units as roughly 4.2 to 5.4 x10^12/L, and there are small sex differences: males tend to have slightly higher counts than females due to testosterone and iron loss with menstruation. The 4.5–5.5 range neatly covers typical adult values in many clinical resources, making it the best benchmark. Values below this range can indicate anemia, while values above may suggest polycythemia or dehydration; interpretation should also consider factors like altitude, smoking, or chronic lung disease.