Red Blood Cell Count (RBC)

Red blood cells (RBC) are made in the bone marrow and contain hemoglobin, a protein that carries oxygen to the tissues in the body. These cells are also known as erythrocytes.

Red blood cell count is a blood test that measures your levels of erythrocytes. This test is most often done as part of a complete blood count (CBC) that also measures other types of blood cells.

RBC count can help diagnose anemia and other conditions that affect red blood cells. If RBC count results are abnormal, additional tests are usually done to diagnose the cause of the high or low level of red blood cells.

Purpose of the test

The purpose of the RBC count is to find out if the number of red blood cells you have is normal or abnormal. RBC count may be included in routine blood testing during a check-up, usually as part of a complete blood count (CBC) measuring the number of red blood cells, white blood cells (WBCs), and hemoglobin in a blood sample.

Measuring RBCs can help diagnose anemia, a condition in which the body doesn’t have enough healthy red blood cells. There are different types of anemia with distinct causes. A low RBC count is a key indicator of anemia, and additional tests can help determine its underlying cause.

RBC count may also be used to help diagnose other conditions that affect red blood cells, such as kidney problems, a type of white blood cell cancer, or problems with the bone marrow.

What does the test measure?

RBC count is the number of RBCs contained in a sample of blood, usually expressed as millions of cells per microliter (cells/mcL).

In a complete blood count, RBCs are measured along with white blood cells (WBCs) and platelets. These cells are made in the bone marrow and released into the bloodstream as they mature. In the blood, these cells are suspended in a fluid called plasma.

Blood consists of 45% red blood cells, less than 1% white blood cells and platelets, and 55% plasma. RBCs contain hemoglobin, a protein that binds to oxygen. In this way, RBCs carry oxygen to the body’s tissues and carry carbon dioxide from the tissues to the lungs to be expelled.

When should I get an RBC count?

RBC count is usually tested as part of a complete blood count, which is a common lab test that can be used to detect or monitor many different health conditions. Your health care provider may order this test:

• As part of a routine check-up
• If you are having symptoms of anemia, such as fatigue, headache, loss of appetite, or problems concentrating
• If you are having other symptoms of blood cell changes, such as fever, infection, or weakness
• When you are receiving treatment that can affect your blood cell counts, such as chemotherapy
• To monitor a long-term health problem that may change your blood count results, such as chronic kidney disease

Your health care provider can explain why an RBC count is being ordered for your situation and help explain what the results mean.

How to get tested

A red blood cell count test is usually ordered by a doctor and requires a blood sample, which is drawn by a health provider or a laboratory technician at an office, hospital, laboratory, clinic, or other medical setting.

Can I take the test at home?

Most CBC and RBC tests are done in a medical setting, and limited options are available for taking these tests at home.

In some cases, you may be able to take an RBC count with a self-collection test. In this type of test, you use an at-home kit to prick your finger and place a drop of blood on a special test paper. You then mail this blood sample to a laboratory where it can be analyzed, and your results are delivered through a website or smartphone app.

How much does the test cost?

The cost of a RBC count depends on where you have the blood sample drawn, the charges by the laboratory where your blood is analyzed, and whether you have insurance coverage. You can ask your doctor, the laboratory, and/or your health insurance provider about costs and whether your plan will cover the blood draw and laboratory testing.

The RBC test requires a blood sample. Most often, blood is drawn from a vein in the inside of the elbow.

Before the test

No preparation is required before having this test. Some medications can affect red blood cell count, so make sure the doctor who ordered your test knows about all of the prescription and over-the-counter medications you are taking.

During the test

There are several steps involved in the blood draw for a RBC count or CBC test:

1. The puncture site on your arm is cleaned to kill any germs and prevent infection.
2. An elastic band is tied around the upper arm to apply pressure so that the veins swell, making them easier to locate. Making a fist also helps to make the veins swell.
3. A needle is inserted into a vein.
4. The blood flows into a vial or tube attached to the needle. Sometimes more than one vial of blood is needed if multiple tests are being done.
5. The pressure is released on the upper arm and the elastic band is removed.
6. The needle is taken out and the spot is covered with a bandage to stop bleeding.

A blood draw usually takes less than 3 minutes. When the needle is inserted, there may be a brief prick or sting of pain, which can range from mild to moderate.

Some people feel nervous or uncomfortable around needles or at the sight of blood. Be sure to tell the person who is drawing blood if you feel nervous or woozy, and they can try to make you as comfortable as possible. Looking away or talking to someone to distract you can sometimes help.

After the test

Once the blood draw is complete, a piece of gauze or bandage is placed over the spot where the needle is taken out. You may be asked to apply gentle pressure to help stop any bleeding. This may also help prevent swelling and bruising.

You can usually remove the pressure after a minute or two. Any pain or throbbing where the needle was removed usually goes away quickly. You may want to keep a bandage on for a few hours, but you can usually go back to your usual activities once the test is over.

Receiving test results

Results can take anywhere from a few hours to a few business days to come back. Results may be sent directly to you and to your doctor. The results may also be available on an online health portal.

You can ask the health care provider who ordered your test for more details about how and when you will receive the results.

Interpreting test results

RBC count is written as a number value in cells per microliter (cells/mcL). The normal range for red blood cells depends on factors like age and sex. RBC can also be affected by elevation in the area where testing is conducted.

Because multiple factors can affect RBC count, it’s important to talk to your doctor to understand what your test results mean.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. In general, reference ranges for adults typically fall between 4 and 6 million cells per microliter of blood. Males typically have a higher reference range.

The expected RBC count in babies, children, and adolescents can vary significantly based on their age. RBC counts are often highest in newborns and decrease through infancy before reaching levels similar to adults during childhood and adolescence.

The typical lifespan of an RBC is 120 days, so they have to be replaced constantly. Erythropoietin is a hormone that is made in the kidneys and is released to stimulate the bone marrow to make more red blood cells. Health conditions that disrupt the normal creation and function of RBCs can cause abnormal RBC count.

A high RBC count may be due to:

• Dehydration
• Stress
• High altitude
• Smoking
• Cardiovascular disease
• Polycythemia vera, which is a disorder of the bone marrow that causes too many red blood cells to be made
• A type of kidney cancer called renal cell carcinoma and other cancers that produce erythropoietin

A low RBC count may be caused by a number of conditions, including:

• Anemia
• Malnutrition
• Pregnancy
• Overhydration
• Hemolysis, which is the breakdown of red blood cells
• Chronic kidney failure
• Severe bleeding or hemorrhage
• Failure of normal blood cell production in bone marrow

Some types of medications can also contribute to an increase or decrease in RBC count.

An RBC count test alone often cannot determine the reason why RBC levels are high or low. Other blood cell counts may be considered in interpreting the significance of RBC levels, and further tests are often needed to diagnose a specific cause of an abnormal RBC count.

Because many different conditions can affect your RBC count, it is important to review your test results with your doctor who can address the most likely explanations for your RBC level.

Do I need follow-up tests?

RBC count is only one test used to help identify a health issue affecting red blood cells. A number of other blood tests may be ordered if your RBC count is abnormal.

For example, if the RBC count is low, test results for hemoglobin and hematocrit, which is the percent of the blood taken up by RBCs, may help to diagnose anemia. If anemia is suspected, RBC indices are tests that help to determine the cause of the anemia.

If the RBC count is high, results of the complete blood count (CBC) can help to diagnose polycythemia, a condition in which there is an increased concentration of hemoglobin and/or hematocrit in the blood.

Follow-up tests are tailored to your situation based on your health history, symptoms, and test results. Your doctor can describe the follow-up tests that may be most appropriate in your case.