What is a Peripheral Blood Smear test? 
A peripheral blood smear test, also referred to as blood smear test, peripheral blood film, blood smear analysis or smear test, is performed to determine the number and shape of red and white blood cells (RBCs and WBCs) and platelets. It also aids in the differential count, ie, identify the number and shapes of different types of WBCs or leucocytes and helps check for any abnormalities in any types of blood cells. The different types of leucocytes include neutrophils, eosinophils, basophils, monocytes and lymphocytes. 

Different blood cells play different vital roles in the body.

  • WBCs fight against infections and are a part of the immune system
  • RBCs or erythrocytes carry oxygen to the various tissues of the body 
  • Platelets are small fragments of blood cells that are essential for blood clotting
  1. Why is a Peripheral Blood Smear test performed?
  2. How do you prepare for a Peripheral Blood Smear Test?
  3. How is a Peripheral Blood Smear test performed?
  4. What do Peripheral Blood Smear test results indicate?

A peripheral blood smear test is performed in individuals experiencing the following symptoms:

Rarely, this test helps detect contact with parasites or its carriers; for example, individuals who reside in an area with a high number of mosquitoes are at a higher risk of developing malaria.
A variety of diseases can affect the appearance as well as the number of different blood cells. Therefore, a peripheral blood smear is useful in the diagnosis of numerous conditions, such as

  • Bone marrow disorders
  • Blood cancer
  • Anaemia
  • Myeloproliferative neoplasms

This test is also valuable for determining the blood cell count after chemotherapy.

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Although no special preparations are required for this test, ask the doctor if you need to fast before going for the test. If you are taking any medicines, including herbs, vitamins and nutritional supplements ensure that your doctor is aware of them. Also, inform the doctor if you are taking any non-prescription drug or illegal drugs.

It is a simple test that involves the collection of blood from a vein in your arm or hands. The blood sample can also be obtained by pricking the finger in adults. A stinging sensation or pain is experienced when the needle is pricked into the skin.

A heel stick is used to collect a blood sample from infants.

Some risks associated with blood tests include infection, bleeding, a feeling of faintness and bruising. Slight soreness may also be experienced at the site of injection.

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Results of this test vary based on the age, sex and medical and clinical status of the individual. Therefore, consulting a doctor is ideal for the correct interpretation of results. A doctor will interpret your results based on the symptoms observed.
Results of a blood smear test may not always diagnose the condition; it only reveals the details of the appearance of blood cells and the presence of any abnormalities in these cells. Though it may often indicate the possibility of an underlying condition. Thus, further tests will be performed to confirm the diagnosis.

Normal results:

Blood cells

Cell size



8 micrometres (µm) diameter

A nucleus is absent in normal mature erythrocytes. The cell itself is pink or red in colour. It is round and flattened in shape with a depression in the middle.

WBCs: These are of two types described below:

Varies in different types of WBCs

 Nucleus is present



 Granules are present

  • Basophils

10-15 µm

It consists of 1% of total leucocytes and is seen rarely. It has purple-black granules.

  • Neutrophils

10-18 µm

Pink or purple granules are present in the cell. These are present in the majority of healthy individuals.

  • Eosinophils

10-15 µm

It consists of 1-3% of leucocytes and has large red-orange granules.



Granules are absent

  • Monocytes


Largest white blood cells

  • Lymphocytes

10-12 µm

A smooth and round nucleus is present in lymphocytes.

Abnormal results: Any variation in the number or appearance of a significant number of RBCs indicates the following conditions:

Conditions that affect the number or appearance of various types of WBCs include:

  • Infection or inflammation, which causes an increase in the numbers of certain types of leucocytes
  • Allergic reactions that affect the number of eosinophils
  • Bone marrow disorders that may cause alteration in the number of leucocytes
  • Blood cancer

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.


  1. Bain BJ. Diagnosis from the blood smear. N Engl J Med. 2005 Aug 4;353(5):498-507 PMID: 16079373
  2. Diego Villa Clé. Blood film in the era of streaming cells Rev Bras Hematol Hemoter. 2017 Oct-Dec; 39(4): 295–296 PMID: 29150098
  3. AS Adewoyin, B Nwogoh. Peripheral blood film- A review Ann Ib Postgrad Med. 2014 Dec; 12(2): 71–79 PMID: 25960697
  4. Gulati G, Song J, Florea AD, Gong J. Purpose and criteria for blood smear scan, blood smear examination, and blood smear review. Ann Lab Med. 2013 Jan;33(1):1-7 PMID: 23301216
  5. Samuel Ricardo Comar, Mariester Malvezzi, Ricardo Pasquini. Evaluation of criteria of manual blood smear review following automated complete blood counts in a large university hospital Rev Bras Hematol Hemoter. 2017 Oct-Dec; 39(4): 306–317 PMID: 29150102
  6. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Blood Smear
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