Peripheral Smear (PS) Test

The peripheral smear test, though basic, is a very important test to diagnose a number of diseases. This test checks the characteristics of blood components (RBCs, WBCs and platelets) to identify any abnormality. These findings help in the diagnosis of multiple blood and blood-related disorders.

In this test, a sample of blood is spread on a specific slide and examined under a microscope to check for various blood parameters. The peripheral smear test has great significance in the diagnosis of many diseases, as it detects abnormalities in blood cells that may indicate underlying health conditions. It can also help to check the therapy response.

Peripheral blood film is advised in conditions where the disease or symptoms indicate a blood disorder or blood-related disorder. It is also prescribed in cases where the diagnosis requires blood film results as supportive evidence.

Generally, RBC abnormalities suggest indications like anaemia, thalassemia, hemolytic anaemia, bone marrow disorders, sickle cell anaemia, etc. WBC abnormalities indicate leukaemia, infections or allergies. Platelet abnormalities include thrombocytopenia (lower count of platelets) or thrombocytosis (higher count of platelets).

In India, there is an alarming status of haematological disorders (blood disorders). Acquired diseases like anaemia show greater presence as compared to inherited disorders like thalassemia. However, the incidence of thalassemia is also considerably high.

Correct diagnoses with precise physical and laboratory examinations constitute the necessary step to tackle this situation. A peripheral smear test is one of the important diagnostic tests performed for haematological disorders. Though there have been many advances in diagnostics, this test retains its function and importance.

Other names of peripheral smear test

• Manual differential or differential slide
• Blood smear analysis
• Blood cell morphology
• Peripheral blood film
• A blood film or smear examination

What does the peripheral smear test detect or measure and who is this prescribed for?

Peripheral blood smear detects any abnormality in blood cells and thus diagnoses the relevant blood or blood-related disorder. This test measures the size, shape and number of blood components, which include RBCs, WBCs and platelets. Some of the conditions it detects are:

• Anaemia: The presence of macrocytes (RBCs of large size) of oval shape indicates megaloblastic anaemia. A greater quantity of hypochromic microcytic RBCs (cells having less colour and of smaller than normal size) are found in iron deficiency anaemia, thalassemia, etc.
• Thrombocytopenia: When there is a lesser number of platelets than normal, the condition is called thrombocytopenia.
• Bacterial infections: If there are a greater number of neutrophils (neutrophilia) in comparison to the general number, a bacterial infection is indicated.

So, the alterations in the morphology of blood cells help to detect multiple disorders.

A peripheral blood smear is prescribed when:

• One shows abnormal CBC (complete blood count) results.
• There are symptoms relative to blood disorders like jaundice, fever, fatigue, bone pain, abnormal bleeding, and pale skin.
• One has a chance of being exposed to ticks.
• One has travelled to developing countries with a chance of contact with parasites like malaria.

Common indications in which peripheral smear is advised include anaemia, thrombocytopenia, unexplained jaundice, congenital haemolytic anaemias, suspected organ failure like renal failure or liver disorder, parasite infection or bacterial sepsis, malignancies, leukaemia, unexplained haemolysis, bone marrow disorders, nutritional anaemia and many more.

To carry out this test, a medical professional will collect blood from a vein of the forearm with a syringe.

Test Preparation

No particular preparation is required for this test. For this test, one needs to visit a medical professional, who will then collect the blood sample for the test. It takes about 5 minutes to collect the blood sample. Upon collection of the blood sample, a small amount is spread on a specific slide, which is then observed under a microscope.

Test inclusions: What parameters are included?

Below are the parameters measured in the peripheral smear test:

Red blood cell morphology:

• Cell size
• Shape
• Colour
• Intracellular inclusions
• Pathologic arrangement

White blood cell morphology:

• Cell counts: Neutrophils, lymphocytes, eosinophils, monocytes and basophils
• Cell size
• Shape
• Colour

Platelet morphology:

• Size
• Count

How frequently should you take the peripheral smear test?

There is no particular frequency established for this test. Based on the recommendation of a medical professional, the test has to be repeated.

What are peripheral smear findings?

Below are the findings of the peripheral smear test:

• Red blood cell morphology: Cell size, shape and colour, intracellular inclusions, pathologic arrangement, Anisocytosis.
• White blood cell morphology: Cell counts (neutrophils, lymphocytes, eosinophils, monocytes and basophils), cell size, shape and colour.
• Platelet morphology: Size and count

Anaemia, Thrombocytopenia, Bone marrow disorders, Leukaemia, Hemolytic anaemia, Parasite

Normal ranges for red blood cells’ characteristics observed in the test:

Normal ranges for white blood cells’ characteristics:

Normal ranges for platelets’ characteristics: