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’s also known as 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 receive. Your tissues need oxygen to function effectively.
According to the American Association for Clinic Chemistry (AACC), the test is almost always a part of a complete blood cell (CBC) test. A CBC test measures the number of all types of components in the blood, including:
- red blood cells
- white blood cells
Your doctor may perform the test if they suspect you have a condition that affects your RBCs or if there’s any sign that you have low blood oxygen. The signs of low blood oxygen include:
- general fatigue
- nutritional deficiencies
A CBC test will often be part of a routine physical exam because it’s a good indicator of your overall health. It may also be performed before a surgery.
If you have a diagnosed blood condition that may affect RBC count or you’re taking any medications that affect your RBCs, your doctor may order the test to monitor your condition or treatment.
An RBC count is a simple blood test performed by a healthcare provider at your doctor’s office. They will draw blood from your vein, usually on the inside of your elbow. The steps involved in the blood draw typically are:
- The healthcare provider will clean the puncture site with an antiseptic.
- They will wrap an elastic band around your upper arm to make your vein swell with blood.
- They will gently insert a needle into your vein and collect the blood in an attached vial or tube.
- They will then remove the needle and elastic band from your arm.
- The healthcare provider will send your blood sample to a laboratory for analysis.
There’s no special preparation required for this test. However, you should tell your doctor if you’re taking medications, including any over-the-counter drugs or supplements.
Talk to your doctor to find out if any other preparation is necessary.
As with any blood test, there’s a risk of bleeding, bruising, or infection at the puncture site. You may feel moderate pain or a sharp pricking sensation when the needle first enters your arm.
According to the Mayo Clinic:
- The normal RBC range in males is 4.32 to 5.72 trillion cells per liter.
- The normal RBC range in females is 3.90 to 5.03 trillion cells per liter.
However, these ranges may vary slightly depending on the laboratory or doctor.
Higher Than Normal
You have erythrocytosis if your RBC count is higher than normal. This may be due to:
- cigarette smoking
- congenital heart disease
- renal cell carcinoma, which is a type of kidney cancer
- pulmonary fibrosis
- polycythemia vera, which is 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 because there’s less oxygen present in the air.
Certain drugs, such as gentamicin and methyldopa, can also increase your RBC count. Be sure to tell your doctor about any medications you take.
Lower Than Normal
If the number of RBCs is lower than normal it may be caused by:
- bone marrow failure
- erythropoietin deficiency, which is the primary cause of anemia in patients with chronic kidney disease
- hemolysis, or RBC destruction, due to transfusion, blood vessel injury, or other causes
- leukemia, which is a cancer of the blood cells
- multiple myeloma, which is a cancer of the plasma cells in bone marrow
- nutritional deficiencies, including deficiencies in iron, copper, folate, and vitamins B-12 and B-6
Certain drugs can also lower your RBC count, especially:
- chemotherapy drugs
Your doctor will discuss any abnormal 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 may need to order additional tests or treatments.