Too many red blood cells can make your blood thicker , which slows blood flow and raises the risk of blood clots. That can lead to serious problems like stroke , heart attack , or organ damage if the cause is not treated.

Quick Scoop

A high red blood cell count is also called erythrocytosis or polycythemia. One important cause is polycythemia vera , a blood cancer in which the bone marrow makes too many red blood cells.

What you might notice

Symptoms can include:

  • Headaches.
  • Dizziness.
  • Blurred or double vision.
  • Fatigue or weakness.
  • Shortness of breath.
  • Itching, especially after a hot shower.
  • Nosebleeds or bleeding gums.

Why it matters

When blood gets thicker, it does not move through vessels as easily, and that makes clots more likely. In more serious cases, the condition can contribute to stroke , tissue damage , and sometimes long-term bone marrow problems.

Common causes

A high red blood cell count can happen because of:

  • Low oxygen levels , such as from lung or heart disease.
  • Smoking.
  • Dehydration.
  • Certain medicines or treatments.
  • Blood cancers , especially polycythemia vera.

When to get help

If you have symptoms of a clot, stroke, or heart attack, seek emergency care right away. If you have persistent symptoms or a blood test showing a high red blood cell count, you should contact a clinician for evaluation.

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