Anabolic steroids and erythropoietin cause high red blood cell counts, according to Mayo Clinic. Erythropoietin, or EPO, injections are given to athletes to increase performance. EPO causes the kidneys to release too much of the protein erythropoietin, which boosts performance in some sports by stimulating red blood cell production.
Red blood cell counts also increase due to long periods at high altitudes because the body compensates for the lower level of oxygen by increasing its red blood cell count, notes Mayo Clinic. Many health conditions also result in high red blood cell counts, including poor heart and lung function, adult congenital heart disease, COPD, kidney cancer, pulmonary fibrosis, heart failure and sleep apnea. Dehydration and carbon monoxide poisoning also cause elevated red blood cell counts. Cigarette smoking leads to higher red blood cell counts because of the lower oxygen levels in the body caused by the effects of smoking.
The medical term for a high red blood cell count is erythrocytosis, which occurs when there are too many red blood cells in the bloodstream, explains Mayo Clinic. Erythrocytosis is diagnosed as over 5.72 million red blood cells per microliter of blood for men and 5.03 million per microliter for women. Red blood cells are produced by bone marrow and transport oxygen from the lungs to the body's tissues.