Trinity Veterinary Hospital
3100 N. Perkins Road, Stillwater, OK, 74075
Phone: (405) 533-0001
Fax: 405-533-0002
Email: welovepets@trinityveterinaryhospital.com
Website: www.trinityveterinaryhospital.com
Complete Blood Count
What is a Complete Blood Count?
The Complete Blood Count, commonly called a “CBC” is a routine blood test that is used in all stages of health and illness. It
is a simple test that gives information about the different cell types in the blood and can indicate the presence of many
forms of disease. Most of the blood cells come from bone marrow, so the CBC can also be used indirectly to assess the
health of the bone marrow (see article on Bone Marrow Collection and Examination).
How is a CBC performed?
A small sample of blood is collected from the pet and placed in a special tube that
prevents the blood from clotting. The sample is then put in a machine called an
automated blood analyzer
analyzer, which counts the different cell types and describes
various characteristics of the cells. In addition, a drop of blood is spread thinly on a
glass slide creating a blood smear. This is stained with special dyes, and examined
under the microscope to look at the appearance of individual cells.
What does a CBC measure?
The CBC provides information about the three types of cells found in blood. They are
red blood cells (also called erythrocytes or red cells
cells), white blood cells (also called
leukocytes or white cells
cells), and platelets (sometimes called thrombocytes
thrombocytes). Details are
reported on the number, size, and shape of each cell type, as well as any variation in appearance.
What are red blood cells and why are they important?
Red blood cells are the most numerous cells in blood by far, and give blood its red color. They are responsible for carrying
oxygen from the lungs to the tissues of the body. They can do this because of a special protein called hemoglobin that is
found in each red blood cell. As blood is pumped through the lung, oxygen moves into the red cells and binds tightly to
hemoglobin. When the blood is pumped out through the body and into the tissues, oxygen is released from hemoglobin
and allowed to leave the red cells to enter the cells of the tissues.
What does the CBC tell us about red blood cells?
a) Numbers:
The CBC reports three different red cell measurements: Red Blood Cell count (RBC), hematocrit (HCT) and hemoglobin
(HGB). These measurements provide information about how many red cells are present and how much hemoglobin is
available. A decrease in either the red cell count or the amount of hemoglobin is called “anemia.” There are many causes for
anemia, and although the CBC may provide clues, further investigation is almost always required to reach a diagnosis. By
comparison, a mild increase in the number of red cells is relatively common and usually indicates that the pet is dehydrated
or excited. This change is usually temporary and is not worrisome. In very rare cases a persistently high red blood cell
count can signal a bone marrow disorder.
b) Size:
The size of the red blood cells sometimes provides clues about a disease. For
example, larger red cells can be seen with vitamin deficiency and bone marrow
disease etc. Smaller red blood cells can be found with iron deficiency and
immune system problems. Sometimes the red cells are normal size, but there
just aren't enough of them. This suggests longstanding illness such as ongoing
kidney disease, persistent inflammation, or cancer.
c) Color and shape:
The color and shape of the erythrocytes are additional details that help in the
diagnosis of disease. For example, an erythrocyte with a bluish tinge is called a
polychromatophilic erythrocyte
erythrocyte(often shortened to polychrome
polychrome); it is a young red cell newly released from the bone marrow
and it is slightly larger and bluer than older red cells. In an anemic animal, finding polychromes in the blood is a good sign
because it signals that the bone marrow is responding to the anemia by working hard to produce new red blood cells.
Sometimes a special dye is used to count polychromes, and the number is reported as a reticulocyte count. This provides
the same information as counting polychromes, but it is more accurate.
There are many red cell shape changes that have been associated with various diseases. The changes are rarely diagnostic
by themselves but they can provide clues to the nature of the underlying disease.
What are white blood cells and why are they important?
White blood cells or leukocytes ("leuko" means 'white') are essential to help protect the body against infectious organisms
such as bacteria and viruses, and also against foreign material that may enter the body.
"Think of white blood cells like the "armed forces" of the body..."
It may help to think of white blood cells as the "armed forces" of the body. Instead of the army, navy, and air force, the
body’s armed forces have five branches represented by different types of white blood cells called neutrophils, lymphocytes,
monocytes, eosinophils, and basophils
basophils. The different groups of leukocytes work independently and in combination,
depending on the problem that is present.
What does the CBC tell us about white blood cells?
a) Numbers:
The automated analyzer counts the total number of white blood cells and reports
a White Blood Cell count (WBC)
(WBC). This gives an indication of the pet's overall level
of protection against infection. The analyzer then subdivides the WBC and counts
the number of leukocytes in each of the five divisions. The resulting five numbers
together are called the “differential.” Changes in the distribution of leukocytes
across the differential can provide information about the type and severity of
inflammation, possible causes of the inflammation, and whether the bone
marrow is able produce enough white blood cells. Sometimes the white blood cell
count is extremely high or extremely low; either of these changes may signal
severe infection or indicate serious bone marrow disease, including cancer.
b) Appearance:
The appearance of leukocytes can indicate whether the body is overwhelmed by infection or is handling a crisis properly.
Leukocyte appearance can indicate the presence of toxins or signal that the immune system has been activated. The
presence of bizarre-looking or abnormal cells is often a sign of serious bone marrow disease including cancer.
What are platelets and why are they important?
Platelets are tiny cell-like structures that are present in large numbers blood and serve as
the first line of defense against bleeding. They are continually on guard to seal
microscopic injuries on the inside of blood vessels, and they are the first to respond to
minor wounds. For example, when you get a skin scratch or paper cut, or prick your finger
with a pin, it is the job of the platelets to stop the bleeding. It is critical to maintain
adequate numbers of platelets in the blood.
What does the CBC tell us about platelets?
a) Numbers:
The automated analyzer reports the number of platelets in the blood, which gives an
indication of the body’s ability to stop minor bleeding. If the platelet count falls below a
certain critical level, then widespread spontaneous bleeding may occur. A low platelet count may be caused by a variety of
diseases such as recent infection, serious systemic illness, immune disorders, or bone marrow disease. An increased
platelet count is commonly associated with simple excitement or exertion, although a high platelet count may be seen when
the marrow is working hard to repair a shortage of platelets. In very rare cases, extremely high platelet counts may indicate
underlying bone marrow cancer.
b) Size:
A platelet’s size is generally related to its age; young platelets are large and plump while older platelets are generally
smaller. The presence of large, plump, young platelets indicates that the bone marrow is actively producing new platelets.
This is an important finding and in a pet with a low platelet count, it is a clue about the underlying disease.
c) Appearance:
Very rarely, bizarre-looking abnormal platelets may be found; these are often a sign of serious bone marrow disease
including cancer.
This client information sheet is based on material written by: Kristiina Ruotsalo, DVM, DVSc, Dip ACVP & Margo S. Tant BSc, DVM, DVSc
© Copyright 2015 LifeLearn Inc. Used and/or modified with permission under license.