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High RBC (Red Blood Cell) count in the blood

Blood test
High RBC (Red Blood Cell) count in the blood
Last update: 02/12/2020

What is a high count of RBC in the blood called?

  • Erythrocytosis

What is the normal RBC count in the blood?

If you need to know which are the RBC reference ranges or you require more information about the role of RBC in the blood, you can visit normal RBC (Red Blood Count) count in the blood

What does a high count of RBC in the blood mean?

The RBC count is a count of the number of RBCs (Red blood Cells) per volume of blood (million/µl). RBCs (Red Blood Cells) are also called erythrocytes and a RBC count above the normal range is called erythrocytosis.

The main causes to develop an erythrocytosis in a blood test are:

  • Polycythemia vera (PV): It is a genetic disease where the bone marrow produces too many blood cells (RBCs, WBCs and platelets).
  • Drugs: Erythropoietin, more commonly known as EPO, is frequently used in sports doping.
  • Hypoxia: If there is an oxygen deficiency due to some respiratory diseases such as COPD or cystic fibrosis.
  • Move to high altitude increases or after increased physical training: In both instances, the underlying reason is a response to an increased need for oxygen.

Erythrocytosis refers to the increase of absolute count of RBCs whereas polyglobulia refers to the relative increase (%) of RBCs volume in relation with blood plasma. In polyglobulia there is an increase in hematocrit (the RBC % in relation with total blood volume). In erythrocytosis there is an absolute elevation of RBC count, but perhaps not an elevation of hematocrit (It can be seen in case of beta thalassemia minor).

It is also important to note the difference between the term polycythemia to indicate an increase in RBC count as well as other blood cells (WBC, platelets, etc.) and erythrocytosis to designate an increase in RBC count alone.

Erythrocytosis or a high RBC count means:

  • Mild RBC count increase (5.5 - 6 million/ µl in adult women and 6.2 - 6.75 million/ µl in adult men):

    RBC count is a bit high, but it is not a matter for concern.

    It may be due to dehydration, tobacco, physical training, live in high altitude or a consequence of some drugs.

    If there is no other test out of the normal range, it is probable that the RBC count returns to normal range in the next assay.

  • Moderate RBC count increase (6 - 8 million/ µl in adult women and 6.7 - 9 million/ µl in adult men):

    RBC count is above the normal range and a visit to your doctor is recommended.

    It may consequence of an increase of erythropoietin production due to pulmonary or heart problems. A kidney cancer is also a possibility.

    If the hematocrit is also high the probability to suffer from thrombosis increases.

  • Marked RBC count increase (> 8 million/ µl in adult women, > 9 million/ µl in adult men):

    RBC count is very high and the main cause is polycythemia vera, a genetic disorder that increase the RBC production in the bone marrow. It also produces too many WBCs and platelets. In polycythemia vera RBC count can reach 11 million/µl with hematocrit above 70%.

    At such high levels, the risk of suffering a blood clot and a cardiovascular disorder (stroke, heart attack, angina pectoris) is very high.

    A marked RBC count increase requires immediate medical care.

Which factors can increase the RBC count in the blood?

There are some health circumstances or drugs than can raise your RBC count:

  • Dehydration (due to excessive sweating, vomiting or diarrhea)
  • Prolonged training
  • High altitude
  • Carbon monoxide poisoning
  • Tobacco
  • Drugs
    • Antibiotics
      • Gentamicin
    • Antihypertensives
      • Methyldopa
    • Danazol
    • Diuretics
    • Erythropoietin (EPO)
    • Anabolic steroids
    • Laxatives
    • Testosterone

Which diseases can increase your RBC count in the blood?

A RBC count level higher than normal may be a sign of the following diseases:

  • Meningioma
  • Cerebellar hemangioblastomas
  • Pheochromocytoma
  • Parathyroid cancer
  • Heart failure
  • Eisenmenger's syndrome
  • Chuvash erythrocytosis

What can I do to lower the RBC count in the blood?

If your RBC count is a bit high, you should:

  • Reduce alcohol and caffeine intake.
  • Give up smoking.

Another possibility is to donate blood or to perform periodically phlebotomy (removal of blood from your vein). The ultimate goal of both procedures is to lower the number of your blood cells and reduce your cardiovascular risk. At the same time if you donate your blood you can help other people.

Where can I find more information about RBC count in the blood?

You can visit our pages about:

Which values are considered a high RBC count in the blood?

The following values are considered to be above the normal range:

IMPORTANT: These levels are expressed in mill/µl (microliter). They are an example of a healthy woman of about 45 years old with no known disease and not taking any medication. The ranges can be different depending on the laboratory or on your personal circumstances.

RBC Count
Mild RBC count increase
5.6 mill./µl5.7 mill./µl5.8 mill./µl5.9 mill./µl6 mill./µl   
Moderate RBC count increase
6.1 mill./µl6.2 mill./µl6.3 mill./µl6.4 mill./µl6.5 mill./µl6.6 mill./µl6.7 mill./µl6.8 mill./µl
6.9 mill./µl7 mill./µl7.1 mill./µl7.2 mill./µl7.3 mill./µl7.4 mill./µl7.5 mill./µl7.6 mill./µl
7.7 mill./µl7.8 mill./µl7.9 mill./µl8 mill./µl    
Marked RBC count increase
8.1 mill./µl8.2 mill./µl8.3 mill./µl8.4 mill./µl8.5 mill./µl8.6 mill./µl8.7 mill./µl8.8 mill./µl
8.9 mill./µl9 mill./µl9.1 mill./µl9.2 mill./µl9.3 mill./µl9.4 mill./µl9.5 mill./µl9.6 mill./µl
9.7 mill./µl9.8 mill./µl9.9 mill./µl10 mill./µl10.1 mill./µl10.2 mill./µl10.3 mill./µl10.4 mill./µl
10.5 mill./µl10.6 mill./µl10.7 mill./µl10.8 mill./µl10.9 mill./µl11 mill./µl11.1 mill./µl11.2 mill./µl
11.3 mill./µl11.4 mill./µl11.5 mill./µl11.6 mill./µl11.7 mill./µl11.8 mill./µl11.9 mill./µl12 mill./µl
Medically reviewed by our Medical staff on 02/12/2020


  • Concise Book of Medical Laboratory Technology: Methods and Interpretations. 2nd Edition. 2015. Ramnik Sood. ISBN: 978-93-5152-333-8. Pag. 214.
  • Laboratory tests and diagnostic procedures with nursing diagnoses (8th ed), Jane Vincent Corbett, Angela Denise Banks, ISBN: 978-0-13-237332-6, Pag. 25.

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