What is a blood smear?

Also Known As: Peripheral Smear, Blood Film, Manual Differential, Differential Slide, Red Blood Cell Morphology, Erythrocyte Morphology, Leukocyte Differential

Formal Name: Peripheral Blood Smear

A blood smear is a sample of blood that's tested on a specially treated slide. For a blood smear test, a laboratory professional examines the slide under a microscope and looks at the size, shape, and number of different types of blood cells. These include:

• Red blood cells, which carry oxygen from your lungs to the rest of your body
• White blood cells, which fight infection
• Platelets, which help your blood to clot

Many blood tests use computers to analyze results. For a blood smear, the lab professional looks for blood cell problems that may not be seen on computer analysis.
Other names: peripheral smear, peripheral blood film, smear, blood film, manual differential, differential slide, blood cell morphology, blood smear analysis

What is it used for?

A blood smear test is used to help diagnose blood disorders.

Why do I need a blood smear?

You may need a blood smear if you have abnormal results on a complete blood count (CBC). A CBC is a routine test that measures many different parts of your blood. Your health care provider may also order a blood smear if you have symptoms of a blood disorder. These symptoms include:

• Fatigue
• Jaundice, a condition that causes your skin and eyes to turn yellow
• Pale skin
• Unusual bleeding, including nose bleeds
• Fever
• Bone pain

In addition, you may need a blood smear if you have been exposed to ticks or have traveled to a developing country, or if your health care provider thinks you have a disease caused by a parasite, such as malaria. Parasites may be seen when a blood smear is looked at under a microscope.

What happens during a blood smear?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparation for a blood smear. If your health care provider has ordered other blood tests, you may need to fast (not eat or drink) for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

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