Third Street
Veterinary Hospital, PC
McMinnville, Oregon 97128
Office phone: (503) 472-9418
Anemia in the Dog
Anemia
is defined as a reduced number of red blood cells or hemoglobin, or both. It is a clinical sign, not a specific
disease. It is a significant finding
because red blood cells, or erythrocytes, are needed to transport oxygen to the
tissues. When the total numbers of red blood
cells are reduced, there can be insufficient oxygen delivery to vital
organs.
Red
blood cells are produced in the bone marrow, or hollow core of the bones, by
specialized cells. Before being
released into circulation, the precursor cells must undergo a specific sequence
of steps to reach full maturity. Once
released by the bone marrow, the red blood cell lives about 120 days in
dogs. Interestingly, the red blood cell
lives much shorter in cats, about 60-70 days.
Anemia
is probably the most frequent laboratory abnormality involving the blood
cells. It is a relatively common
finding in dogs of all ages and breeds.
Clinical Signs
The
most easily observed sign of anemia is a loss of the normal pink color of the
gingiva (gums). Anemic dogs also have
little endurance so they seem very weak or tired. Pale gingiva and lethargy make us want to perform some tests on
blood to document anemia. Sometimes,
anemia can cause the heart rate to elevate and a heart murmur to develop. If the anemia is caused by red blood cell
destruction, the skin may have a yellow tint (jaundice or icterus). When certain cancers are the underlying
cause of anemia, the lymph nodes, spleen, intestines, or liver might be enlarged.
Diagnosis and
Evaluation
Initial Tests
The
initial tests performed on blood are needed to determine the severity of the
anemia and the ability of the bone marrow to respond to the anemia. The most common test for anemia is the
packed cell volume (PCV); it is also called the hematocrit. A blood sample is placed in a centrifuge to
separate the red blood cells from the plasma (the liquid part of the
blood). This takes only a few drops of
blood and can be performed in about five minutes. The normal PCV of the dog is 35%-50%; anemia is defined as a PCV
below 35%.
A
more complete assessment of the red blood cells can be calculated by very
sophisticated instrumentation; a number of specific measurements can be
provided. These include hemoglobin, as
well as the diameter and volume of individual red blood cells.
Responsiveness
of the bone marrow to the anemia is evaluated by the reticulocyte count. The reticulocyte is a young adult red blood
cell. It has not quite completed all of
the steps to maturation. A rough index
of the reticulocyte numbers can be gleaned by examining a blood smear. The precise count is easy to determine by
mixing a small amount of blood with a special stain and then re-examining the
blood smear. It is generally preferable
to have a reticulocyte count that reflects the ability of the bone marrow to
respond to the anemia; this is called a “regenerative anemia.” When the marrow appears unresponsive based
on reticulocyte numbers, this is called a “non-regenerative anemia.”
Additional
Tests
Several
other tests are usually indicated for complete evaluation of the dog with
anemia. These are described below.
A
careful study of the blood smear is important to look for parasites that might
be causing red blood cell destruction and abnormal cells that could indicate
leukemia. A test to look for
immune-system destruction of red blood cells, called a “Coombs Test,” may also
be done at this time.
A
bone marrow biopsy or aspirate is a procedure that recovers a small sample of
cells from the bone marrow for evaluation by the veterinary pathologist. Studying these cells can give valuable
information about the cause of some anemias and the condition of the bone
marrow. Sometimes it is prudent to give
the bone marrow a few days to respond to the anemia if there is a suspicion of
recent blood loss. When this is the
case, a bone marrow aspirate may be temporarily postponed. In some situations, it is clear that the
anemia is long-standing and a bone marrow evaluation should be done as soon as
possible.
A
biochemical profile and urinalysis are other important tests for anemic
dogs. These tests evaluate organ
functions and electrolyte levels. They
will often provide important information about the total health of the
dog. A fecal exam is also important for
identification of parasites in the intestinal tract that might be causing blood
loss.
Causes/Transmission
Several
tests are important for an anemic dog because there are many diseases that
cause anemia. These are grouped into 1)
diseases that cause blood loss, 2) diseases that cause hemolysis (red blood
cell breakdown), and 3) diseases that decrease the production of red blood
cells.
The main
causes of blood loss in dogs include:
Trauma
or injury that severs blood vessels or internal organs
Parasites
such as fleas, ticks, and hookworms
Tumors
of the intestinal tract, kidneys, and urinary bladder
Diseases
that prevent proper clotting of blood
The main
causes of hemolysis in dogs include:
Autoimmune
disease
Blood
parasites
Chemicals
or toxins
Neoplasia
(cancer)
The main
causes of bone marrow suppression in dogs include:
Any
severe, chronic disease
Very
poor nutrition or nutritional imbalances
Autoimmune
disease
Chemicals
or toxins
Neoplasia
(cancer)
It
is noteworthy that while iron deficiency anemia is a common finding in people,
especially women, it is uncommon in dogs and only occurs secondary to some form
of chronic blood loss.
Treatment
If
your dog's anemia is so severe that it is life threatening, a blood transfusion
is needed. This may be performed
immediately after a blood sample is taken for testing. The main purpose of a blood transfusion is
to stabilize the dog long enough that a determination of the cause of the
anemia can be made.
Further
treatment will be determined once the underlying disease has been diagnosed.
Prognosis
The
prognosis is dependent upon identification of the underlying cause and a
positive response to appropriate therapy.
Sometimes, the prognosis cannot be given for a few days because all of
the diagnostic tests may not be completed.