What Is a Red Blood Cell Count Test?

Medically Reviewed by Poonam Sachdev on November 05, 2021

A red blood cell count test measures how many red blood cells (RBCs) your blood contains. The red blood cells, or erythrocytes, have hemoglobin — a protein that transports oxygen to all parts of your body.

The amount of oxygen transported to your body parts depends on your red blood cell count. 

Other names for the red blood cell count test are RBC count and erythrocyte count. The test is done as a part of a complete blood count (CBC) to identify several health conditions.

Why Do I Need RBC Testing?

A health care professional does RBC testing during the complete blood count (CBC) test.

The RBC test provides essential information about the types and amounts of cells in the blood. 

Men usually have a higher red blood cell count than women. The level of red blood cells decreases as a person ages.

The normal RBC count is:

  • Men: 4.7 to 6.1 million RBCs per microliter of blood
  • Women: 4.2 to 5.4 million RBCs per microliter of blood
  • Children: 4.0 to 5.5 million RBCs per microliter of blood

Any number lower or higher than the normal RBC count could indicate a medical condition.

An RBC test is done when the doctor identifies signs of weakness or fatigue during a routine checkup. You may also need this test to examine specific health conditions that are usually not obvious. 

These health conditions include internal bleeding, kidney diseases, anemia, and others. 

Your doctor usually asks you to do this test to determine any change in your normal RBC count. 

How Is the Red Blood Cell Count Test Done?

A blood sample is required for this test. A health care professional uses a needle to draw blood from a vein in your hand or arm.

What Should I Do Before the Red Blood Cell Test?

There are no specific guidelines to follow before going for the RBC testing. The doctor usually asks you to:

  • Avoid intense exercise.
  • Relax and reduce stress.
  • Drink plenty of water.
  • Avoid or delay taking certain medicines.

You must inform your doctor about all the medicines and supplements you are taking.

What Will My Red Blood Cell Count Test Results Show?

Several factors may affect your test results. They include your age, health history, gender, and the method used for the test. 

Your test results show the number of red blood cells in your blood. Test results don't always mean that you have a health issue.

What If I Have a Low RBC Count?

‌Several health conditions lead to the production of fewer red blood cells in your body. Some low RBC count causes include:

  1. Certain medications, including antiretroviral drugs for HIV infection, chemotherapy drugs, and more
  2. Blood loss
  3. Anemia
  4. Leukemia, a type of blood cancer
  5. Chronic kidney diseases
  6. Cirrhosis, scarring of the liver
  7. Vitamin B-12 or folate deficiency
  8. Stomach ulcers
  9. Lupus, a condition when your immune system attacks your body
  10. Hypothyroidism, an underactive thyroid
  11. Inflammatory bowel disease (IBD)
  12. Hodgkin lymphoma, cancer caused by white blood cells
  13. Multiple myeloma, another type of cancer originating from white blood cells
  14. Lead poisoning
  15. Rheumatoid arthritis

What If I Have a High RBC Count?

‌Many health conditions can increase your body’s red blood cell count. High RBC count causes may include: 

  • Heart failure, causing low oxygen levels in the blood
  • Congenital heart disease, a natural heart condition
  • Polycythemia vera, a condition in which the bone marrow produces high levels of red blood cells
  • Kidney tumors
  • Lung diseases, such as emphysema and pulmonary fibrosis 
  • Carbon monoxide exposure due to excessive smoking
  • Living at a high altitude
  • Dehydration
  • Presence of performance-enhancing drugs, like synthetic testosterone or erythropoietin

What Factors Can Affect My Red Blood Cell Count Test Results?

Several factors can affect your RBC count, including:

  • Dehydration, less intake of water
  • Overhydration, high intake of water
  • Stress
  • Altitude
  • Pregnancy
  • Certain medications
  • Your position during the test

Are There Any Risks to the Red Blood Cell Count Test?

The red blood cell count test is done with a needle, so it has some risks. These can be bleeding, bruising, infections, and dizziness. The pain of needle pricking is usually mild, but the area can become sore afterward. There are no severe risks in RBC testing.

Show Sources


‌Cleveland Clinic: "Complete Blood Count," "High Red Blood Cell Count."

‌Mayo Clinic: "Cirrhosis," "High Red Blood Cell Count," "Low Hemoglobin Count."

‌NHS: "Red Blood Cell Count."

University of Rochester Medical Center: "Red Blood Cell Count," "What Are Red Blood Cells?"

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