What is blood count?

Your blood count can reveal hidden information about your health and risk for disease. Knowing what a blood count is and how it affects you is critical to your overall health.

What Is a Complete Blood Count?

Your blood is made up of red blood cells, white blood cells, hemoglobin, and platelets.

Red blood cells are responsible for sending oxygen through your body and helping to discard carbon dioxide, while white blood cells enable your body to fight off infections. Hemoglobin is the oxygen-carrying protein present in red blood cells.

A complete blood count also includes the measurement of hematocrit, which is the proportion of red blood cells to the plasma. Platelets control any bleeding by helping your body form clots.

  • Red blood cells carry oxygen throughout the body.
  • White blood cells fight infection and disease.
  • Hemoglobin is the oxygen-carrying protein in red blood cells.
  • Platelets aid in blood clotting.

When undergoing a complete blood count, your doctor is measuring the number and types of these blood cells in your body. Your blood count can help your doctor pinpoint diseases such as anemia or cancer, clotting issues, and infection. A blood count also can help determine if you have an immune system disorder.

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When Do You Need a Blood Count Test?

There are various reasons your doctor may order a blood count test, including to:

  • Evaluate your overall health.
  • Monitor an ongoing health problem.
  • Diagnose a specific health condition.
  • Offer medical treatment for an illness or disease.

What to Expect When Getting a Blood Count Test

Unless your doctor asks that you fast before your complete blood count test, you should typically be able to eat and drink normally. If your doctor requires additional tests for your blood, then you may be asked to fast.

A complete blood test is similar to donating blood. A lab technician will clean your skin with an antiseptic wipe, place a band around your upper arm to swell blood in the veins, then insert a needle into a vein to draw the predetermined number of vials.

Complete blood tests often do not require more than two or three vials. In the cases of infants, the lab technician will use the heel of the child to draw the blood instead of the forearm. Test results should be made available to you within a few hours to a day from when your blood is drawn.

Normal Blood Count Ranges

Normal blood count ranges depending on your gender and age. In general, the normal range for a red blood cell count is 4.5 to 5.5 million cells/mm3 if you’re male and 4 to 5 million cells/mm3 if you’re female.

For white blood cell count, the normal range is 5,000 to 10,000 cells/mm3, and for platelets, the typical range is 140,000 to 400,000/mm3.

For hemoglobin the normal range is 135-175 grams/L in men, and 120-155 grams/L in women.

Children and pregnant women may have different normal counts, so talk to your doctor about the results.

What Does a Blood Count Reveal About Your Health?

A blood count test provides a variety of information about your health.

Low red blood cell count

A low red blood cell count could mean you have anemia. A few common causes of low red blood cell count includes:

  • Iron deficiency anemia.
  • Other types of anemia.
  • Heavy menstruation.
  • Radiation or chemotherapy treatments.
  • Hemolysis or the autoimmune destruction of blood cells.

Low white blood cell count

A low white blood cell count could signify neutropenia, a condition that puts you at a higher risk for infection. Common causes of low white blood cells includes:

  • Aplastic anemia
  • Sarcoidosis
  • Chemotherapy
  • Lupus
  • Leukemia
  • Rheumatoid arthritis
  • Viral infections
  • Tuberculosis

Abnormal platelet count

An abnormal platelet count may indicate that you have a blood clotting disorder, such as thrombocytopenia. Chemotherapy and radiation treatment also can cause a low platelet count. Platelets are produced in the bone marrow, and production can be reduced by factors including:

  • Anemia.
  • Viral infections.
  • Heavy alcohol consumption.
  • Chemotherapy drugs.
  • Leukemia and other cancers.

If you’re interested in finding out your blood count, ask your doctor if a complete blood count is right for you. To learn more about blood count testing, visit the UPMC Heart and Vascular Institute website.


Editor's Note: This article was originally published on , and was last reviewed on .

About Heart and Vascular Institute

The UPMC Heart and Vascular Institute has long been a leader in cardiovascular care, with a rich history in clinical research and innovation. As one of the first heart transplant centers in the country and as the developer of one of the first heart-assist devices, UPMC has contributed to advancing the field of cardiovascular medicine. We strive to provide the most advanced, cutting-edge care for our patients, treating both common and complex conditions. We also offer services that seek to improve the health of our communities, including heart screenings, free clinics, and heart health education. Find an expert near you.