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Blood Smear

(Peripheral Blood Smear)

What Is a Blood Smear?

Red blood cells, white blood cells, and platelets can be seen through a microscope when they are smeared on a slide. The blood is allowed to dry and is stained with a special dye. The color, number, size, and shape of the cells and platelets can help a doctor find blood disorders or diseases.

Reason for the Test

This test is done when a problem with your blood is suspected.

Type of Sample Taken

A blood sample will be taken from a vein in the arm

Prior to Collecting the Sample

A recent blood transfusion and other procedures can affect the results of this test. Talk with your doctor about your health and treatment plans.

During the Sample Collection

You will be asked to sit. An area inside your elbow will be cleaned with a wipe. A large band will be tied around your arm. The needle will be put in a vein. A tube will collect the blood from the needle. The band on your arm will be taken off. After the blood is collected, the needle will be removed. Gauze will be held on the site to help stop bleeding. You may also be given a bandage. This test takes about 5-10 minutes.

In other situations, your finger may be pricked with a needle. A drop of blood will be squeezed onto the glass to create the smear. A band-aid will be put on the site of the needle prick.

After Collecting the Sample

After the blood sample is taken, you may need to stay seated for 10 to 15 minutes. If you are lightheaded, you may need to stay seated longer. When you feel better, you can leave.

A bit of blood may ooze from the vein beneath the skin. It will cause a bruise. A bruise will usually fade in a day or two.

Call your doctor right away if you have redness, swelling, lasting bleeding, or pain.


It will take several days to get your results.

There are many size, color, and shape differences linked to health problems. Your number of red and white blood cells may also point to a problem. A trained technician is the only person who can assess the health and quality of your blood cells on the slide. A doctor will use the blood smear results, the results of other tests, and knowledge of your symptoms and health to make a diagnosis. Some problems may be:

  • Leukemia and other types of cancers
  • Lead poisoning
  • Sickle cell disease
  • Liver disease
  • Problems with bone marrow that causes cells to release before they are fully developed
  • Some types of anemia or red blood cell defects
  • Thrombocytopenia—low platelet count
  • Chemotherapy side effects
  • Parasitic infections—some types can be seen by blood smear

Talk to your doctor about your test results. A test may point to an illness that you do not have. It can also miss an illness that you may have. The doctor will check your symptoms and all test results before making a diagnosis.


Gulati G, Song J, Florea AD. Purpose and criteria for blood smear scan, blood smear examination, and blood smear review. Ann Lab Med. 2013 Jan;33(1):1-7. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3535191. Accessed May 13, 2019.

Blood smear. Lab Tests Online—American Association for Clinical Chemistry website. Available at: http://labtestsonline.org/understanding/analytes/blood-smear/tab/test. Updated December 19, 2018. Accessed May 13, 2019.

Last reviewed March 2019 by EBSCO Medical Review Board James P. Cornell, MD  Last Updated: 5/13/2019