Blood Smear
Reviewed
Also called: peripheral smear, peripheral blood film, smear, blood film, manual differential, differential slide
A blood smear is a test that's used to help diagnose and monitor a wide variety of blood disorders and other conditions that affect your blood.
Specimen: Blood
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. This usually takes less than five minutes. Sometimes, the blood sample will be taken by pricking your finger with a needle. When testing a baby, 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
Your blood smear results will describe what your blood cells look like and how many there are. The results will also show anything else that's unusual about your blood, for example, if any parasites were found.
- Red blood cell results not normal: Red blood cell results that aren't normal, may be a sign of conditions, such as: anemia, sickle cell disease, hemolytic anemia, a type of anemia that causes your body to destroy red blood cells faster than it makes them, thalassemia, bone marrow disorders. Limitation: The results of a blood smear alone usually can't diagnose a medical condition. Next step: If your blood smear results are not normal, your provider may order more tests to help find the cause.
- White blood cell results not normal: White blood cell results that aren't normal may be a sign of conditions, such as: infection, leukemia, bone marrow disorders. Limitation: Other conditions can also cause abnormal blood smear results, including: severe illness, stress, blood transfusions. Next step: Your provider will use your test results combined with your medical history, symptoms, and the results of other tests to make a diagnosis.
- Platelet results not normal: Platelet results that aren't normal may be a sign of conditions, such as: thrombocytopenia, a lower-than-normal number of platelets. This may increase your risk of bleeding. Having too many platelets can cause blood clots to form in your blood vessels (the tubes that carry blood in your body). Limitation: The results of a blood smear alone usually can't diagnose a medical condition. Next step: Talk with your provider to learn more about your results.
- 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
If your blood smear 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
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.