Red Blood Cell Count (RBC)

Written by Jacquelyn Cafasso | Published on August 7, 2012
Medically Reviewed by George Krucik, MD

What is a Red Blood Cell Count?

A red blood cell count is a blood test that your doctor uses to find out how many red blood cells (RBCs) you have in your blood. It is also called an erythrocyte count.

The test is important because RBCs contain hemoglobin, which carries oxygen to your body’s tissues. The number of RBCs you have can affect how much oxygen your tissues are receiving. Your tissues need oxygen to function effectively.

Why Will Your Doctor Order the Test

According to the National Institutes of Health, the test is almost always performed as part of a complete blood cell (CBC) test. (NIH) This measures the amount of all types of components in the blood, including:

  • red blood cells
  • white blood cells
  • hemoglobin
  • hematocrit
  • platelets

Your doctor may perform the test if he or she suspects you have a condition that affects your RBCs, or if there is any sign that you have low blood oxygen. Such signs might be anemia, bruising, general fatigue, and/or nutritional deficiencies.

Often, a CBC test will be part of a routine physical examination, since it is a good indicator of your overall health. It may also be performed before a surgery.

If you have been previously diagnosed with a blood condition that may affect RBC count or you are taking any medications that affect your RBCs, your doctor may order the test to monitor your condition or treatment.

How Is the Test Performed?

An RBC count is a simple blood test performed by a healthcare practitioner at your doctor’s office. Blood will be drawn from a vein, usually at the inside of your elbow. The steps involved in the blood draw typically are:

  • The puncture site will be cleaned with an antiseptic.
  • A healthcare provider will wrap an elastic band around the upper arm in order to make your vein swell with blood.
  • A needle will be gently inserted into the vein, and blood will collect in an attached vial or tube.
  • The elastic band will be removed from your arm.
  • The blood sample will be sent to a laboratory for analysis.

How Should You Prepare for the Test?

There is no special preparation required for this test. However, you should tell your doctor if you are taking any medications, including over-the-counter drugs or supplements.

Talk to your doctor to find out if any other preparation is required.

What Are the Risks of Taking the Test?

As with any blood test, there is a risk of bleeding, bruising, and/or infection at the puncture site. You may feel moderate pain or a sharp pricking sensation when the needle is first inserted into your arm.

Normal Results: Standard Ranges of RBCs | Normal Range

According to the Mayo Clinic, the general normal ranges by gender are as follows (Mayo Clinic). However, these may vary slightly depending on the laboratory or doctor:

  • Males: 4.32 to 5.72 million cells per microliter
  • Females: 3.9 to 5.03 million cells per microliter

What Does an Abnormal Result Mean?

Higher Than Normal:

If your RBC is higher than normal, it is called erythrocytosis. This may be caused by:

  • cigarette smoking
  • congenitalheart disease
  • dehydration
  • renal cell carcinoma (kidney cancer)
  • pulmonary fibrosis
  • polycythemia vera (a bone marrow disease that causes overproduction of RBCs and is associated with a genetic mutation)

When you move to a higher altitude, your RBC count may increase for several weeks, since there is less oxygen present in the air.

Certain drugs, such as gentamicin and methyldopa, can also increase RBC count. Be sure to tell your doctor about any medications you may take.

Lower Than Normal:

Below-average numbers of RBCs may be caused by:

  • anemia
  • bone marrow failure
  • erythropoietin deficiency (the primary cause of anemia in patients with chronic kidney disease)
  • hemolysis (or RBC destruction) due to transfusion, blood vessel injury, or other causes
  • bleeding
  • leukemia (cancer of the blood cells)
  • malnutrition
  • multiple myeloma (cancer of the plasma cells in bone marrow)
  • nutritional deficiencies (including iron, copper, folate, and vitamins B12 and B6)
  • pregnancy

Certain drugs can also lower your RBC count, especially chemotherapy drugs, chloramphenicol, hydantoins and quinidine.

What If I Have Abnormal Results?

Your doctor will discuss any abnormalities in your results with you. A high or low RBC count may help identify the cause of your symptoms. Depending on your results and your situation, your doctor will order the additional tests or treatments necessary to return you to health.

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