Understanding the Red Blood Cell (RBC) Count

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The red blood cell (RBC) count is used to measure the number of oxygen-carrying blood cells in a volume of blood. It is one of the key measures we use to determine how much oxygen is being transported to cells of the body.

An abnormal RBC count is often the first sign of an illness that may either be undiagnosed or without symptoms. At other times, the test can point the doctor in the direction of a diagnosis if there are symptoms, such as shortness of breath or fatigue, which cannot be readily explained.

Red blood cell count

Complete Blood Count

Typically speaking, an RBC count is less useful on its own to diagnose a medical condition. Instead, it is most often performed as part of a more comprehensive test called a complete blood cell (CBC) count which measures the composition cells in a blood sample. They include:

  • Red blood cells (RBC) which transport oxygen to cells of the body
  • White blood cells (WBC), which are a part of the immune system
  • Hemoglobin (Hb), a protein which carries oxygen and carbon dioxide molecules
  • Platelets (PLT), the cells responsible for blood clotting
  • Hematocrit (Hct), the ratio of RBC to the total volume of blood

Based on the composition of blood cells, doctors can better know where to focus their investigation and which areas they can probably avoid.

An RBC count may also be used to monitor treatment for blood disorders or medications that affect your RBC. This is especially true for cancer and cancer chemotherapy, both of which can have a detrimental cause-and-effect impact on blood counts.

Normal Ranges

An RBC count is the number of red blood cell per a particular volume of blood. It may be reported in millions of cells per microliter (mcL) of blood or in millions of cells per liter (L) of blood.

The "normal" range can sometimes vary by population. Many reference values will be far higher in high-altitude cities like Denver and far lower in low-altitude areas like the Gulf Coast. As such, the ranges cannot be considered hard-and-fast values but rather, as the name suggests, a reference point.

The RBC count reference range varies by sex and age:

  • Women: 4.2 to 5.4 million/mcL
  • Men: 4.7 to 6.1 million/mcL
  • Children: 4.1 to 5.5 million/mcL

High or Low RBC Counts

When the RBC count is higher or lower than the reference range, it alerts the physician that there could be an underlying condition. The other values from the CBC will be considered, as well as other diagnostic tests.

High RBC Count Causes

A high RBC count tells us that there has been an increase in oxygen-carrying cells in blood. In some cases, this may indicate that the body is compensating for some condition that is depriving the body of oxygen, in others, the cause may be related to diseases or drugs that alter the production of RBCs.

Low RBC Count Causes

A low RBC count indicates a decrease in oxygen-carrying cells in the blood, otherwise known as anemia. The causes can be numerous, ranging from infections and deficiencies to malnutrition to malignancies, including:

  • Kidney failure
  • Thyroid problems
  • Bleeding, internal or external
  • Leukemia, a type of blood cancer
  • Drug side effects, including chemotherapy
  • Multiple myeloma, a type of cancer affecting plasma cells
  • Erythropoietin deficiency, a kidney hormone that promotes RBC growth
  • Deficiencies in iron, folate, vitamin B12, or vitamin B6
  • Hemolysis, the abnormal breakdown of red blood cells
  • Pregnancy


Treatment of an abnormal RBC count is typically focused on treating the underlying condition, whether it be an infection, injury, cancer, or a genetic disorder.

If, on the other hand, the cause is related to a nutritional deficiency, medication use, or a chronic condition, there may be things you can do to not only improve your blood count but your overall health, as well.

High RBC Count Treatment

If you have a high RBC count:

  • Exercise to improve heart and lung function.
  • Eat less red meat and iron-rich foods.
  • Avoid iron supplements.
  • Keep yourself well hydrated.
  • Avoid diuretics, including coffee and caffeinated drinks.
  • Stop smoking, especially if you have COPD or pulmonary fibrosis.
  • Avoid the use of steroids, erythropoietin, and other performance-enhancing drugs.

Low RBC Count Treatment

If you have a low RBC count (including anemia):

  • Maintain a healthy, balanced diet.
  • Take a daily vitamin and iron supplement, if needed.
  • Exercise regularly to improve heart and lung function.
  • Stop smoking.
  • Avoid aspirin, which reduces clotting and can cause slow chronic blood loss.
  • Take your thyroid medications as prescribed if you have thyroid problems.
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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. George-Gay B, Parker K. Understanding the complete blood count with differential. J Perianesth Nurs. 2003;18(2):96-114. doi:10.1053/jpan.2003.50013

  2. Leukemia & Lymphoma Society. Understanding blood counts.

  3. National Heart, Blood, and Lung Institute. Iron-deficiency anemia.

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