Test Quick Guide

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 the number of erythrocytes circulating in your blood. This test is almost always done as part of a complete blood count (CBC) that also measures other types of blood cells.

Anemia is a condition that results from a decrease in the number of RBCs. Elevated RBC counts are seen in other conditions where there is low oxygen levels, certain drugs, kidney disease, or bone marrow overproduction. If your RBC count results are abnormal, additional tests are usually done to diagnose the cause of the high or low level of red blood cells.

About the Test

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. An RBC count may be included in routine blood testing during a medical check-up and is always included as part of a complete blood count (CBC) measuring the number of red blood cells, white blood cells (WBCs), and platelets in addition to the amount of hemoglobin present in the red blood cells.

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 anemias with distinct causes. A low RBC count is a key indicator of anemia, thus requiring 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 (number of RBCs x106/µL).

In a complete blood count (CBC), 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.

In a healthy human weighing between 150 to 180 pounds, the total blood volume is about 1.2 to 1.5 gallons (4.5 to 5.7 liters). Of this total volume plasma makes up almost 55% while red blood cells (RBCs) make up approximately 44%. White blood cells (WBCs) and platelets are  1% or less of the total volume.  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 back to the lungs to be expelled.

When should I get an RBC?

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.

Finding an RBC

How can I get an RBC test?

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

Can I take the test at home?

CBC tests include an RBC count and are done in a medical setting with limited options available for taking these tests at home. While a blood sample may be collected in a microdevice at home, but  then has to be mailed to a laboratory for evaluation with results available several days later. One at-home CBC device that has recently received FDA approval uses a finger prick to obtain a drop of blood that is placed on a special test strip and immediately inserted into a portable device for analysis.

How much does the test cost?

The cost of a RBC test depends on the type of test you get, where you have the blood sample drawn, the charges by the laboratory where your blood is analyzed, and whether you have insurance coverage.

Taking an RBC

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

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. In some cases when other tests are ordered, your healthcare provider may suggest fasting before the blood draw.

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, and allowed to dry.
  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.

The blood draw procedure usually takes only a few minutes to complete. 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 will be applied to the puncture area to minimize any additional bleeding. A bandage is then placed over the area. Any pain or throbbing after the needle has been removed usually goes away quickly. You may want to keep the bandage on for a few hours to minimize any bruising, but you can usually go back to your usual activities once the test is over.

Red Blood Cell Count (RBC) Test Results

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 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 (number of RBCs x106/µL). The normal range for red blood cells depends on factors like age and sex  and can vary slightly among different laboratories due to the equipment used in different laboratories. In general, reference ranges for adults typically fall between 4 and 6 million cells per microliter of blood. Males typically have a higher number of RBCs than females.

The number of RBCs can also be affected by elevation in the area where testing is conducted. At higher altitudes, less oxygen is available thus the need for your body to increase the number of RBCs that can deliver the required amount of oxygen.

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

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
  • Low oxygen levels (COPD, pulmonary fibrosis, sleep apnea, cardiovascular disease)
  • Polycythemia vera, an abnormal proliferation (increase) of RBCs, which is a disorder of the bone marrowA type of kidney cancer called renal cell carcinoma and other cancers that produce erythropoietin
  • Certain drugs (Anabolic steroids, Erythropoietin, Gentamicin, Testosterone, Methyldopa)

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

  • Anemias
    • Iron deficiency anemia – lack of iron intake
    • Vitamin deficiency anemia – vitamin B12 or folate
    • Aplastic anemia – bone marrow stops red cell production
    • Bone marrow disease-associated anemia – such as leukemia
    • Hemolytic anemia- shortened RBC life span due to secondary disease
    • Sickle cell anemia and Thalassemia – inherited red disorders
  • Malnutrition
  • Pregnancy
  • Overhydration
  • Hemolysis, the physical act of red blood cells breaking apart and releasing hemoglobin
  • Chronic kidney failure
  • Severe bleeding or hemorrhage
  • Failure of normal blood cell production in bone marrow
  • Certain autoimmune diseases
  • Chronic alcoholism
  • Toxic chemical exposure
  • Genetic/family history

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. A blood smear is often requested to identify any abnormally sized and/or irregularly shaped RBCs that may be present

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. Some questions you may want to ask your doctor about your RBC results include:

  • What does my red blood count indicate about my health?
  • Were the results from the test abnormal? If so, how should I address the abnormality?
  • Are there any diagnoses to be made based on my red blood count results?
  • Will any follow-up tests be needed based on my results?
  • Given my RBC results, is there anything that you would suggest I do to improve my health?



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