Peripheral Blood Smear

A peripheral blood smear (PBS) is a blood test that helps healthcare providers diagnose issues like blood cancer, blood disorders and infections. Some blood tests use machines to analyze blood samples. With a peripheral blood smear, a lab technician treats the sample with chemicals that highlight changes. Then, a hematologist or hematopathologist views the sample through a microscope. The microscopic view may spot changes in your blood that certain conditions cause.

Why would I have this test?

A healthcare provider may order this blood test if:

• A routine complete blood count detects issues with your blood cells or platelets. Your provider may order a PBS to learn more.
• You have symptoms like fatigue, fever or bruising. These may be symptoms of blood cancer, a blood disorder or an infection.
• Your provider wants to know more about your bone marrow and blood cells because you may need a stem cell transplant.
• You’re receiving treatment. A PBS is one way your provider can check whether treatment is working.

What does a peripheral blood smear show?

The test may detect issues with your blood cells and platelets. These cells and platelets play different roles:

• Red blood cells: These cells carry oxygen from your lungs to your tissues. Your red blood cells carry carbon dioxide back to your lungs. When you exhale, you’re getting rid of the carbon dioxide.
• White blood cells: These cells are part of your immune system that help protect your body from infection. There are five different white blood cell types. Each type fights infection in different ways.
• Platelets: These are cell fragments that help your blood form clots. Too few platelets may be a sign of cancer, infections or other health problems. A peripheral blood smear may show changes in the size and shape of your blood cells and platelets. These changes may be signs of blood disorders or blood cancer.

What diseases can a peripheral blood smear detect?

Certain diseases may cause unusually high or low blood cell counts or abnormal blood cells. Examples include:

• Leukemia: This is a cancer of blood and bone marrow. It happens when genetic mutations (changes) turn normal cells in your bone marrow into abnormal ones.
• Myelodysplastic syndrome: This syndrome includes cancers that genetic changes cause. The changes affect your blood stem cells so your body can’t make healthy mature white blood cells, red blood cells and/or platelets.
• Anemia: You have anemia when your body doesn’t have enough healthy red blood cells.
• Heart failure: A higher-than-normal red blood cell count may be a sign of heart failure.
• Lymphoma: This disease happens when a type of white blood cell becomes cancerous.
• Autoimmune diseases: A low white blood cell count or a low platelet count may be a sign of an autoimmune disease. These diseases happen when your immune system accidentally launches attacks on your body instead of protecting it.
• Malaria: You develop malaria if a mosquito that carries a parasite bites you. The bite delivers parasites into your bloodstream. A peripheral blood smear may find the parasites in your blood.

It’s important to remember that a peripheral blood smear doesn’t diagnose disease. It gives your healthcare provider important information about your blood cells and platelets. Your provider may do other tests to learn more about your health.

It’s normal to feel anxious about follow-up tests that check for serious health issues. Your provider will explain why they want a more detailed look at your blood. Don’t hesitate to ask questions.

How does a peripheral blood smear work?

The test itself involves a phlebotomist taking a small sample of your blood. You don’t need to fast or do anything to get ready. They’ll collect blood in a tube and send it to a lab. There, a lab technician will:

1. Spread a drop of your blood onto a glass plate to make a thin film.
2. Treat blood with chemicals that bring out specific details about your blood cells and platelets.
3. A hematologist or a hematopathologist checks your blood cells and platelets through a microscope for any abnormalities or changes.
4. Share test results with your healthcare provider.

What do peripheral blood smear results mean?

Your results will depend on the reason why you have the test. For example, the results may show why you have certain symptoms.

When should I call the doctor?

Some people have a peripheral blood smear because they have certain symptoms. If that’s your situation, contact your healthcare provider if your symptoms worsen or you have new ones.

Are peripheral blood smear results positive or negative?

No, they’re not. That’s because this test isn’t designed to find a specific issue. It simply gives healthcare providers more information about blood cells and platelets.

What’s the difference between a CBC and a peripheral blood smear?

With a complete blood count (CBC), a machine analyzes the blood sample to count your blood cells and platelets. It also measures blood cell and platelet size. With a peripheral blood smear, a healthcare provider uses a microscope to look for changes in your blood cells and platelets.