Red Blood Cell (RBC) Count

A red blood cell (RBC) count 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 make 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 may allow you to get treatment even before you have symptoms.

Why this test is done

You may get this test as part of a CBC, which is often included in a routine checkup. You may also need this test if you are getting treatment that might affect your blood cell counts, such as chemotherapy, to monitor health conditions, such as chronic kidney disease, or if you have symptoms of a low or high red blood cell count.

Symptoms of a low red blood cell count may include:

• Shortness of breath
• Weakness or fatigue
• Headache
• Dizziness
• Arrhythmia (a problem with the rate or rhythm of your heartbeat)
• Pale skin

Symptoms of a high red blood cell count may include:

• Headache
• Dizziness
• Vision problems

How to prepare

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

Sample type

Blood

Other names for this test

erythrocyte count, red count, RBC Count