Blood Smear

Why this test may be ordered

• Abnormal complete blood count (CBC) results
• Symptoms of a condition that affects blood cells, such as fatigue, jaundice, unusual bleeding, easy bruising, fever, bone pain, or swollen lymph nodes
• Monitoring treatment for a condition that affects blood cells, such as anemia or blood cancer
• Symptoms of parasitic diseases like malaria or babesiosis if you have traveled to areas where these are common

Preparation and collection

You don't need any special preparation for a blood smear. If your provider has ordered other blood tests, you may need to fast (not eat or drink) for several hours before the test.

A health care professional will take a blood sample from a vein in your arm using a small needle. Sometimes the sample is taken by pricking your finger. For babies, the heel is pricked.

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

Understanding results

The results of a blood smear describe the appearance and number of your blood cells. A normal result means your blood cells look normal in size, shape, and number. An abnormal result may indicate a variety of conditions, but a blood smear alone cannot diagnose a disease.

• Normal: Your blood cells appear normal in size, shape, and number. This suggests no significant blood disorder. Limitation: A normal result does not rule out all conditions. This test alone cannot diagnose a disease. Next step: If symptoms persist, further testing may be needed. Your provider will interpret results in the context of your health.
• Abnormal: Abnormalities in red blood cells, white blood cells, or platelets may indicate conditions such as anemia, sickle cell disease, infection, leukemia, bone marrow disorders, or thrombocytopenia. Parasites may also be seen. Limitation: This test alone cannot diagnose a specific condition. Results must be combined with your medical history, symptoms, and other tests. Next step: Your healthcare provider will order additional tests to determine the cause of the abnormal findings.

• A blood smear alone cannot diagnose a disease. Abnormal results require additional testing and must be interpreted together with your medical history, symptoms, and other tests.
• The quality of the sample and preparation can affect results, but this is managed by laboratory professionals.

What to do next

Your provider will use your blood smear results combined with your medical history, symptoms, and the results of other tests to make a diagnosis. If your results are not normal, your provider may order more tests to help find the cause. Talk with your provider to learn more about your results.

• Do you have symptoms such as fatigue, jaundice, unusual bleeding, easy bruising, fever, bone pain, or swollen lymph nodes?
• Have you traveled to areas where malaria or babesiosis is common?
• Have you had a complete blood count (CBC) test recently, and were the results abnormal?
• Are you currently being treated for a condition that affects your blood cells, such as anemia or blood cancer?

Evidence source

U.S. National Library of Medicine: Blood Smear