The range for a normal red blood cell count is 4.5 to 5.5 million cells per microliter for men and 4 to 5 million cells per microliter for women, according to WebMD. Healthy children and babies should typically have between 3.8 and 6.1 million cells per microliter.
Doctors refer to having a low red blood cell count as anemia, which may result from a number factors, including heavy menstrual bleeding, stomach ulcers, and lack of folic acid and vitamin B12, explains WebMD. Certain diseases may also cause anemia, including colon cancer, inflammatory bowel disease, Addison's disease, thalassemia and sickle cell disease.
A high red blood cell count, or polycythemia, can result from changes in water content in the body due to dehydration, diarrhea, vomiting or sweating. Some diseases may also cause polycythemia, including lung disease, kidney disease, liver disease and certain forms of heart disease.