A high red blood cell (RBC) count usually means the body is making extra cells to carry more oxygen, or there is a problem in the bone marrow causing overproduction.

What “high red blood cells” means

  • A high RBC count is often called erythrocytosis or polycythemia and is usually picked up on a complete blood count (CBC).
  • Labs look at hemoglobin, hematocrit, and RBC number; if they are above the lab’s reference range, it is considered high.

Common everyday causes

  • Dehydration : Losing fluid (vomiting, diarrhea, sweating, not drinking enough) makes blood more concentrated, so RBCs appear high even though total cells may be normal.
  • Living at high altitude or spending long periods there : Thinner air means less oxygen, so your body makes more RBCs to compensate.
  • Smoking and sleep apnea : Both lower oxygen levels in the blood, which can trigger extra RBC production.
  • Intense or performance-focused training with certain drugs : Use of anabolic steroids or erythropoietin (EPO) can raise RBCs to improve performance.

Medical conditions that raise RBCs

  • Lung and heart diseases : COPD, emphysema, pulmonary fibrosis, congenital heart disease, and heart failure can all reduce oxygen and push the body to make more red cells.
  • Kidney and liver problems : Some kidney cancers or kidney disease cause excess EPO, and some liver diseases (like fatty liver) are linked with high RBC counts.
  • Bone marrow disorders : Polycythemia vera is a blood cancer where the bone marrow itself makes too many RBCs, often due to an acquired mutation.

Symptoms and why it matters

  • High RBCs can make blood thicker, which may cause headaches, dizziness, blurred vision, fatigue, and a ruddy or flushed face.
  • Very thick blood can increase the risk of clots, which is why persistent or very high values should be evaluated and monitored by a clinician.

What to do next

  • If a lab report shows high RBCs, a clinician usually:
    1. Repeats the test and checks hydration and recent illnesses or medications.
2. Reviews symptoms, smoking status, sleep quality, altitude exposure, and exercise/drug use.

3. Orders further tests (oxygen levels, imaging, EPO levels, or bone marrow–related tests) if the elevation is persistent or high.

If your or someone else’s results are high, it is important to discuss them with a healthcare professional rather than self-diagnosing, because the cause can range from simple dehydration to conditions that need specific treatment.