A blood film—or peripheral blood smear—is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood films are examined in the investigation of hematological (blood) disorders and are routinely employed to look for blood parasites, such as those of malaria and filariasis.
A blood smear is a blood test used to look for abnormalities in blood cells. The three main blood cells that the test focuses on are:
- Red cells, which carry oxygen throughout your body
- White cells, which help your body fight infections and other inflammatory diseases
- Platelets, which are important for blood clotting
The test provides information on the number and shape of these cells, which can help doctors diagnose certain blood disorders or other medical conditions.
Irregularities in the number or shape of your red blood cells can affect how oxygen travels in your blood. These abnormalities are often caused by a mineral or vitamin deficiency, but they can also be caused by inherited medical conditions, such as sickle cell anemia. White blood cells are an integral part of your body’s immune system, which is a network of tissues and cells that help your body fight infection. Having too many or too few white blood cells can indicate a blood disorder. Disorders affecting these cells often result in the body’s inability to eliminate or control infections or other inflammatory problems.
The blood smear test is often done to diagnose conditions that are causing:
- Unexplained jaundice
- Unexplained anemia (low levels of normal red blood cells)
- Abnormal bruising
- Persistent flu-like symptoms
- Sudden weight loss
- Unexpected or severe infection
- Skin rashes or cuts
- Bone pain
How to Identify?
Before the test, it’s important to tell your doctor about any prescription or over-the-counter medications, supplements, and vitamins you’re currently taking. Certain medications can affect your test results. Additionally, if you’re regularly taking anticoagulant therapy, such as warfarin, (Coumadin), you will be at risk for increased bleeding associated with the blood draw. You should also tell your doctor about any existing medical conditions, such as haemophilia. Certain medical disorders, regular blood product transfusions, and the presence of certain type’s blood cancer will produce abnormalities on the blood smear result. It’s important to discuss these matters with your doctor before the blood smear to avoid a possible diagnostic error.
The blood smear is a simple blood test, first cleans and sterilizes the injection site with an antiseptic. They then tie a band above the venous site where your blood will be drawn. This causes your veins to swell with blood. Once they find a vein, the phlebotomist inserts a needle directly into the vein and draws blood. Most people feel a sharp pain when the needle first goes in, but this quickly fades as the blood is drawn. Within a couple of minutes, the phlebotomist removes the needle and asks you to apply pressure to the site with gauze or a cotton ball. They next cover the puncture wound with a bandage, after which you’re free to leave.
A blood test is a low-risk procedure. However, minor risks include:
- Fainting from the sight of blood due to vasovagal syncope
- Dizziness or vertigo
- Soreness or redness at the puncture site
What to Do?
A blood smear is considered normal when your blood contains a sufficient number of cells and the cells have a normal appearance. A blood smear is considered abnormal when there’s an abnormality in the size, shape, colour, or number of cells in your blood. Abnormal results may vary depending on the type of blood cell affected.
Red blood cell disorders include:
- Iron-deficiency anemia
- Sickle cell anemia
- Haemolytic uremic syndrome
- Polycythaemia rubra vera
Disorders related to white blood cells include:
- Acute or chronic leukemia
- HIV, a virus that infects white blood cells
- Hepatitis C virus infection
- Parasitic infections
- Fungal infections
- Other lymphoproliferative diseases
Disorders affecting platelets include:
- Myeloproliferative disorders
A blood smear can also indicate other conditions, including:
- Liver disease