A normal red blood cell count ranges from 4.7 to 6.1 million cells per microliter in males and from 4.2 to 5.4 million cells per microliter in females, states MedlinePlus. Normal values differ slightly depending on the laboratory and measurements used, so patients should discuss individual results with their doctor.
Cigarette smoking, certain heart conditions, dehydration, low blood oxygen levels and bone marrow problems may lead to high red blood cell counts, notes MedlinePlus. Moving to a higher altitude also causes red blood cell counts to temporarily rise. Low red blood cell counts are sometimes caused by pregnancy, bleeding, anemia, leukemia and malnutrition. Chemotherapy drugs and quinidine are also capable of decreasing the number of red blood cells.