Red blood cell count (RBC)

A red blood cell count (RBC) measures the number of red blood cells, also known as erythrocytes, in your blood. Red blood cells are made in your bone marrow, the spongy tissue inside your large bones. They contain hemoglobin, an iron-rich protein that carries oxygen from your lungs to every cell in your body. Your cells need oxygen to grow, reproduce, and produce energy for you to function. An RBC count that is higher or lower than normal is often the first sign of an illness. So the test can allow you to receive treatment even before you have symptoms.

Other names: erythrocyte count, red count, RBC count

A red blood cell count (RBC) is almost always part of a complete blood count (CBC), a set of tests that measure the number and type of cells in your blood. Measuring RBCs is used to help diagnose red blood cell disorders, such as anemia, a condition in which your body doesn't make enough healthy red blood cells.

You can take this test as part of an NFS, which is often included in a routine exam. You may also need this test if you are receiving treatment that may affect your blood cell levels, such as chemotherapy, to monitor health conditions, such as chronic kidney disease, or if you have symptoms of low or high levels of red blood cells.

Symptoms of low red blood cells may include:

• Shortness of breath
• Weakness or fatigue
• Headaches
• Vertigo
• Arrhythmia (a problem with the rhythm or frequency of your heart beat)
• Pale skin

Symptoms of high red blood cells may include:

• Headaches
• Vertigo
• Vision problems

You don't need special preparations for a red blood cell count (RBC).

There are very few risks in taking a blood test. There may be slight pain or bruising where the needle was inserted, but most symptoms go away quickly.

Your results will show if you have a normal red blood cell count or if your red blood cell count is too low or too high.

Conditions that can cause a low red blood cell count may include:

• Anemia
• Leukemia, a type of blood cancer
• Malnutrition, a condition in which your body does not receive the calories, vitamins, and/or minerals needed for good health
• Multiple myeloma, a cancer of the bone marrow
• Kidney failure
• Blood loss due to injury or other problems
• Alcohol Use Disorder (AUD)
• Pregnancy

Conditions that can cause a high red blood cell count may include:

• Dehydration
• Heart disease
• Polycythemia vera, a condition where your bone marrow makes too many red blood cells
• Scarring of the lungs, often due to smoking
• Lung disease
• Kidney cancer
• Sleep apnea, a disorder that causes you to stop breathing repeatedly during sleep

Improper use of certain medications for athletic performance (such as anabolic steroids) and living at a high altitude can also lead to high red blood cell counts.

Talk to your health care provider if you have questions about your results. Your provider will consider your symptoms, medical history, and other blood test results to understand your red blood cell count results.

Learn more about lab tests, reference ranges, and understanding results.

If the results show that you have low or high levels of red blood cells, you may need additional tests to help your doctor make a diagnosis. These may include:

• Reticulocyte count, which measures the number of reticulocytes in your blood. Reticulocytes are immature red blood cells (still developing). This test helps to check if your bone marrow is making the right amount of red blood cells.
• Iron tests, which measure the levels of iron in your blood. Iron is essential for the production of red blood cells.
• The vitamin B test, which measures the quantity of one or more B vitamins in your blood. B vitamins are important for the production of red blood cells and for keeping your body healthy.

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