A high red blood cell (RBC) count, medically called erythrocytosis or polycythemia, means you have more red blood cells than normal circulating in your bloodstream
. This condition causes your blood to be thicker than usual, which can increase the risk of blood clots
What it means when your RBC count is high
- Response to low oxygen: Your body may produce more red blood cells to compensate for low oxygen levels in the blood, which can happen due to lung diseases (like COPD, pulmonary fibrosis), sleep apnea, heart failure, or living at high altitudes
- Dehydration: Loss of plasma volume from dehydration concentrates red blood cells, causing a falsely elevated RBC count
- Smoking: Smoking introduces carbon monoxide, reducing oxygen delivery and stimulating red blood cell production
- Bone marrow disorders: Conditions like polycythemia vera cause the bone marrow to produce too many red blood cells independently of oxygen levels
- Kidney-related causes: Kidney tumors or diseases can increase production of erythropoietin, a hormone that stimulates RBC production
- Other causes: Certain cancers, anabolic steroid use, and genetic conditions can also elevate RBC count
Symptoms of high RBC count
Some people have no symptoms, but others may experience:
- Fatigue or weakness
- Headaches
- Dizziness or lightheadedness
- Shortness of breath
- Blurred vision
- Flushed skin
Summary
A high red blood cell count indicates your body is producing or retaining more red blood cells than normal. It often signals underlying issues such as low oxygen levels, dehydration, smoking effects, or bone marrow disorders. Because thickened blood raises clot risk, further medical evaluation is important to identify and treat the cause
. Normal RBC ranges are approximately 4.7 to 6.1 million cells/mcL for men and 4.2 to 5.4 million cells/mcL for women, though exact values vary by lab
