Study Of Blood Film

Blood Film

Also known as: Peripheral blood smear, manual differential, red blood cell morphology

Formal name: Peripheral blood film

Related tests: FBC, differential, RBC, WBC, platelet count, reticulocyte count, haemoglobin, haemoglobin variants

The Test

1. How is it used?
2. When is it requested?
3. What does the test result mean?
4. Is there anything else I should know?

How is it used?

A blood film was once prepared on nearly everyone who had a full blood count (FBC). With the automated blood cell counting instruments currently used, an automated  differential is also provided. However, if the presence of abnormal WBCs, RBCs or platelets is suspected, a blood film, examined by a trained eye, is still the best method for identifying immature and abnormal cells.
There are many diseases, disorders and deficiencies that can have an effect on the number and type of blood cells produced, their function and their lifespan. Although usually only normal mature cells are released into the bloodstream, circumstances can force the bone marrow to release immature and/or malformed cells into the blood. When a significant number of abnormal cells are present, they can indicate disease and prompt the doctor to do further testing.

When is it requested?

The blood film is primarily used in blood cell populations when a FBC with differential, performed with an automated blood cell counter, shows the presence of abnormal or immature cells. It may also be used when a doctor suspects a deficiency, disease or disorder that is affecting blood cell production, such as an anaemia, decreased or abnormal production of cells in the bone marrow, or increased cell destruction. A blood film may also be rquesed when a patient is being treated or monitored for a blood cell-related disease.

 

What does the test result mean?

Findings from the blood film test do not always give a diagnosis and often indicate the presence of an underlying condition and its severity and suggest the need for further diagnostic testing. Blood film findings may include:

 

RBC (Red blood cells)
Normal, mature red blood cells are uniform in size (7 µm) and do not have a nucleus as do most other cells. They are round and flattened like a doughnut with a depression in the middle instead of a hole (biconcave). With routine staining, due to the haemoglobin inside the RBCs, they appear pink to red in colour with a pale centre. While not every RBC will be perfect, the presence of many cells that are different in shape or size may indicate a more severe problem. There may be one or more irregularities present and may include:

• Anisocytosis - variable sizes of red cells. The presence of smaller RBCs (<7 µm) is referred to as microcytosis and RBCs larger than 7 µm is macrocytosis.
• Poikilocytosis - various shapes of red cells. These may include echinocytes, acanthocytes, elliptocytes, keratocytes, sickle cells, target cells, teardrop cells (dacrocytes), smear cells (also known as smudge or basket cells), and schistocytes.

WBC (White Blood Cells)
White blood cells have a nucleus surrounded by cytoplasm. All WBCs come from bone marrow stem cells. In the marrow, they change into two groups: myeloid and lymphoid cells. They then mature into five different types of WBCs.

• Granulocytes – the three types of cell making up this group are distinguished by granules of characteristic size and colour in their cytoplasm.
• Neutrophils - cells that have cytoplasm with pink or purple granules. They compose the majority of WBCs in a healthy adult. They increase in standard inflammation, such as with bacterial infections or in rheumatoid arthritis.
• Eosinophils  - are easily recognised in stained smears with their large, red-orange granules. Generally low in number (1-3%). They may increase in number with allergies and parasitic infections.
• Basophils - all have large, black granules and are the least often seen type of WBC (1%). Increased numbers of basophils are not often encountered but may be elevated in certain leukaemias, chicken pox,ulcerative colitis , or after an immunisation.
• Monocytes - are usually the largest of the WBCs (12-20 µm) and are often referred to as scavenger cells (phagocytes). They can ingest particles such as cellular debris, bacteria, or other insoluble particles.
• Lymphoid cells - lymphocytes are smaller in size (10-12 µm) and have a homogeneous cytoplasm and a smooth, round nucleus. These cells are responsible for the production of antibodies (immunoglobulins) or have complicated roles in organising the responses of other white blood cells or in recognising and attacking germs or even cancer cells

Platelets:-
These are cell fragments that come from large bone marrow cells called megakaryocytes. Upon release from the bone marrow, they appear as fragments in the peripheral blood. When there is blood vessel injury or other bleeding, the platelets become activated and begin to clump together to form aggregates which is the beginning of a blood clot. You must have a sufficient number of platelets to control bleeding. If there are too few, the ability to form a clot is impaired and can be life-threatening. In some people, too many platelets may be produced, which interferes with the flow of blood and increases a person's risk of developing a blood clot. These same people may also experience bleeding because many of the extra platelets may be dysfunctional even though they appear normal.
Details of platelet investigation is usually part of a FBC. An abnormally low number or high number of platelets may be further evaluated by preparing a peripheral blood film to visualise any anomalies in shape or size directly.

Is there anything else I should know?

Some examples of situations or conditions that may affect or invalidate results of a blood film include:

·  Patient has received a recent blood transfusion

·  Patient has elevated levels of protein

·  Clotted blood specimen

·  Blood collected in wrong specimen tube or not enough blood collected

·  Blood film not prepared or stained correctly

·  Sample too old for preparation of film

END