CBC DIFF PLT-W SMEAR
Also known as
Peripheral Smear, Blood Film, Manual Differential, Differential Slide, Red Blood Cell Morphology. Erythrocyte Morphology, Leukocyte Differential
This test is ordered by the doctor to assess the performance and density of red blood cells, white blood cells, and platelets. It is also used to differentiate between the different types of white blood cells present in the blood and to identify their composition in the blood. The test also aids in the diagnosis, detection, and monitoring of a number of deficiencies, diseases, and disorders associated with blood cell production, function, and lifespan.
The test may be ordered for a variety of reasons. It is ordered by the doctor when the complete blood count or the automated white blood cell test results are abnormal. It may also be ordered by the doctor when he or she thinks that you have signs and symptoms associated with conditions afflicting your blood cells.
A blood sample is drawn from your arm using a syringe.
There is no special preparation needed for the test.
The blood smear test evaluates the cells which are present in the blood. This includes three main components, namely red blood cells , also known as RBCs, white blood cells, also known as WBCs, and platelets, also known as PLTs. The test helps in detecting a number of conditions and diseases, ranging from leukemia to infections and anemia. Blood cells are produced by and reach maturity in the bone marrow. They are released by the bone marrow into the bloodstream as needed after they mature. Red blood cells are also known as erythrocytes. Made in the bone marrow, they are released in the blood cell when they mature. The primary function of red blood cells is to carry oxygen around the body. They contain a protein called hemoglobin which enables them to do so. A red blood cell lasts up to 120 days. The bone marrow must consistently produce red blood cells in order to replace those which have aged or have degraded or lost through injury and bleeding. There are a variety of disorders that can cause a decline in the production of red blood cells and shorten their lifespan. In some cases, heavy bleeding may occur. Red blood cells have a uniform size and shape, but their appearance can be deformed by factors like deficiencies of vitamin B12, iron, and folate. White blood cells, on the other hand, are also known as leukocytes. These cells are present in the bloodstream, the tissues, and the lymphatic system. White blood cells constitute an essential part of the body’s immune system, which fights against foreign invaders to protect the body. White blood cells play a pivotal role in protection against infections, inflammations, and allergic reactions. There are five categories of white blood cells, each of which performs a different function. These include monocytes, eosinophils, neutrophils, lymphocytes, and basophils. White blood cells are present in the blood at a continuum in stable numbers. However, this number may change in response to what is going on in the internal environment of the body. When there is an infection in the body, the bone marrow may produce a more significant number of neutrophils to attack the bacterial infection. In the case of allergens, there may be a greater number of eosinophils present in the body. Diseases also alter the number of white blood cells present in the body; in leukemia, the uniformity of cells also changes, as white blood cells, which are abnormal, multiply rapidly. Platelets are also called thrombocytes. These are small cell fragments that circulate in the blood and are crucial for normal blood clotting. In the case of injury, platelets clump together at the site of the wound to form a temporary plug. They also release signals which prompt the clumping of additional cells at the site until the injury heals. Low platelets in the blood can increase the risk of bleeding and bruising.
A blood smear involves a drop of blood being spread in a thin layer on a glass slide. A special stain is added to the blood and the blood cells on the slide or examined and assessed. Nowadays, automated digital systems allow laboratorians to examine blood smears efficiently. A small drop of blood on the slides contains nearly millions of red blood cells, thousands of white blood cells, and hundreds of thousands of platelets. The average examination compares the size, shape, and general appearance of white blood cells to the established appearance of normal cells. It also evaluates the five different categories of white blood cells and measures their relative percentages in the blood. The smear also evaluates the size, shape, and color of the red blood cells and estimates the number of platelets present. There are a number of diseases and conditions which can impact the appearance and number of blood cells. The results of the smear test are evaluated and used to support results from additional tests. For instance, if red blood cells are pale in color and small in size in comparison to reference cells, then other test results can be utilized to diagnose some kind of anemia.
Normally, the blood smear is ordered by the doctor as a follow-up test when a CBC with differential results point to the presence of atypical, abnormal, or immature cells. The doctor may also order the test when the patient is exhibiting signs and symptoms that suggest a condition affecting blood cell production or lifespan, such as
- Weakness, fatigue
- Pale complexion
- Unexplained jaundice
- Fever
- Excessive bleeding episodes, easy bruising, or frequent nose bleeds
- Enlargement of the spleen
- Bone pain
The results of the blood smear test are not diagnostic itself. They merely point to a possibility or presence of some underlying condition, which paves the way for additional testing. The results are often interpreted in conjunction with the CBC and other tests, as well as signs and symptoms of the patient and their history. The result of the blood smear includes a description of the trifecta of abnormalities that may have been identified by the slide. Abnormalities in the appearance of red blood cells such as anisocytosis (variable sizes of red blood cells), poikilocytosis (various shapes of red blood cells), and Anisopoikilocytosis (difference in size and shape). These abnormalities may indicate the presence of the following:
- Anemia
- Hemoglobin variants including sickle cell anemia and thalassemia
- Leukemia
- Myeloproliferative or myelodysplastic neoplasms
- Bone marrow disorders
- Infections and/or inflammation can lead to an increase in certain types of WBCs
- Bone marrow disorders - depending on which type of disorder it is, the absolute or relative numbers of white blood cells may increase or decrease
- Allergies have an impact on the number of eosinophils
- Leukemia, myelodysplastic syndrome, or myeloproliferative neoplasm — immature white blood cells like blasts may appear in the blood smear. If blasts appear in a blood smear, they may point to a serious bone marrow disease. They can be found in other cases, such as when the bone marrow is recovering or regenerating from chemotherapy or, as another example, stimulated by a medication prior to stem cell collection.
