A high red blood cell count is an increase in a type of cells made in bone marrow and found in blood. The main job of red blood cells is to move oxygen from the lungs to the rest of the body. Health conditions that limit oxygen can cause a rise in red blood cell count. Other conditions can cause the body to make more red blood cells than it needs.

What's thought of as a high red blood cell count varies at different labs.

For adults, the usual range tends to be:

• 4.35 to 5.65 million red blood cells per microliter (mcL) of blood for men.
• 3.92 to 5.13 million red blood cells per mcL of blood for women.

For children, the usual range depends on age and sex.