Definition

A high red blood cell count is an increase in oxygen-carrying cells in your bloodstream. Red blood cells transport oxygen from your lungs to tissues throughout your body. A high red blood cell count can result from a condition that limits your oxygen supply or a condition that directly increases red blood cell production.

The definition of a high red blood cell count varies from one medical practice to another. A normal range in adults is generally considered to be 4.35 to 5.65 million red blood cells per microliter (mcL) of blood for men and 3.92 to 5.13 million red blood cells per mcL of blood for women. In children, the threshold for high red blood cell count varies with age and sex.

Causes

High red blood cell count may be caused by low oxygen levels, kidney disease or other problems.

Low oxygen levels

Your body may increase red blood cell production to compensate for any condition that results in low oxygen levels, including:

• Heart disease (such as congenital heart disease in adults)
• Heart failure
• A condition present at birth that reduces the oxygen-carrying capacity of red blood cells (hemoglobinopathy)
• High altitudes
• COPD (chronic obstructive pulmonary disease) exacerbation — worsening of symptoms
• Pulmonary fibrosis (scarred and damaged lungs)
• Other lung diseases
• Sleep apnea
• Nicotine dependence (smoking)

Performance-enhancing drugs

Certain drugs stimulate the production of red blood cells, including:

• Anabolic steroids
• Blood doping (transfusion)
• Injections of a protein (erythropoietin) that enhances red blood cell production

Increased red blood cell concentration

• Dehydration (If the liquid component of the blood (plasma) is decreased, as in dehydration, the red blood cell count increases. This is due to the red blood cells becoming more concentrated. The actual number of red blood cells stays the same.)

Kidney disease

Rarely, in some kidney cancers and sometimes after kidney transplants, the kidneys might produce too much erythropoietin. This enhances red blood cell production.

Bone marrow overproduction

• Polycythemia vera
• Other myeloproliferative disorders

When to see a doctor

A high red blood cell count is usually found when your doctor has ordered tests to help diagnose a condition you have. Talk to your doctor about what your test results mean. A high red blood cell count and results from other tests may indicate the cause of your illness. Or your doctor may suggest additional tests to monitor your condition.