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Veterinary
Hematology 101 Website
Back To The Basics So You Can Become An Expert and Make Sound
Clinical Decisions
Lon Bartoli, BSN, AHT, VCLS, EMT
Veterinary Hematology is more than just blood cells. Blood,
highly functional and truly definitive,
does much more than provide for the transport of cellular
metabolites and waste products. Blood is made up of four major
components: Plasma, Red Blood Cells, White Blood Cells, and
Platelets.
Each component possesses its own diagnostic significance in the
veterinary clinical setting.
Without blood, you have no viable mammal life. Therefore without
blood, the clinician has no valid
clinicalpicture of disease-state. To appreciate
the value of blood, the clinician should examine each individual
component of blood separately to gain an appreciation for the
clinical significance and diagnostic value of veterinary
hematology in their practice. Anemia will also be discussed.
Plasma
Plasma carries blood and blood proteins. Aside from a high water
content, plasma also contains
dissolved salts, calcium, sodium, magnesium, and potassium.
Plasma contains clotting factors
and on exposure to air it will clot. Serum is the clear fluid
that separates from clotted whole
blood and clotted plasma. Plasma comprises approximately 20% of
the animal body’s extracellular fluid. Most plasma protein
molecules are too large to pass through the capillary walls into
the interstitial space. The small amount of protein that can
pass through the capillary walls is primarily taken up by the
lymph nodes and eventually returned to the circulation.
The Majority of the plasma proteins are produced in the liver.
Plasma proteins form three major
chemical groups (fractions) and have varying functions.
*albumin - approximately 60%
*fibrinogen - approximately 4%
*globulins - approximatly 36% over three subfractions (IgA, IgB,
& IgG)
The relative proportions of plasma proteins can vary in certain
diseases and these variations can
be clinically useful in determining proper IV therapy. Albumin
is the smallest of the plasma proteins and easily passes through
capillary walls. In kidney disease, large amounts of albumin are
excreted through damaged kidney tubules and can be detected in
the urine.
Functions of the plasma proteins include :
Intravascular collid osmotic pressure. Maintains fluid and
electrolyte levels.
Transport of insoluble substances allowed by protein binding
processes
Contribution towards the plasma viscosity
Inflammatory response via microbe fighting antibodies
Protein storage reserve
Clotting
Protection from infection via plasma gamma globulins
Plasma also contains inorganic ions, which are important in
regulating cell function and
maintaining homeostasis. As an example, depletion of potassium
may occur following severe
diarrhea and vomiting. Potassium is an essential element of cell
excitability. Sharp decreases in
potassium will cause muscle weakness and cardiac abnormalities.
Similar problems may cause
sodium depletion. Subtherapeutic sodium levels in the plasma
will result in the volume of
extracellular fluid to decrease which will lead to a drop in
blood pressure causing lethargy,
dizziness, weakness and fainting.
Plasma carries a wide range of substances including dissolved
gasses left over from the
respiratory exchange cycle (mostly CO2). Blood carries oxygen
because it does not have an
affinity for plasma related to its water solubility.
Nutrients, the most abundant being glucose, are carried in the
blood plasma as a source of
fuel for cellular metabolism. Amino acids, fatty acids,
triglycerides, cholesterol and vitamins
are also carried by plasma. Urea, uric acid, creatinine from the
kidneys, bilirubin from the gall
bladder and other waste materials are also transported by
plasma. Plasma proteins carry
hormones, such as cortisol and thyroxine. The plasma also
carries certain drugs and ETOH.
Platelets
Platelets are the result of cellular fragments shed from the
megakaryocyte while in the bone
marrow. Platelets considered cell fragments rather than actual
cells, play a critical role in blood
clotting. When an injury to the body occurs, a chemical
substance is released at the site of injury.
Platelets are able to quickly adhere to this chemical and begin
to form alliances with other
platelets and clotting factors. This alliance is the body’s
defense against bleeding to death.
Platelets are also significant in forming diagnostic clues to
the blood smear and can be useful at
guiding the clinician in care planning, treatment and further
diagnostic steps. Platelet morphology
together objective data can be indicative of bleeding disorders
and leukemia.
RBCs
Red Blood Cells, seemingly basic, are created and have the sole
purpose of keeping the mammal
alive by carrying oxygen to the tissues and white blood cells
out of the bone marrow and into circulation. Red Blood Cells
along with other blood components are present in nearly every
portion of the body. When there is not enough blood in the body,
anemia occurs and the animal begins to have clinical signs. It
becomes imperative that clinicians immediately identify the
etiology of anemia in order to help define or refine treatment.
In doing so, the clinician will examine the blood smear and
available objective data in order to quickly determine whether
the anemia present as defined by a low pack cell volume (PCV) is
one of production, consumption, sequestration or destruction. We
will be discussing the cellular size, shape, color and other
diagnostically significant data present in various states of
anemia to aid the clinician in accurate slide evaluation.
WBCs
The white Blood Cell (WBC) plays an important role in the animal
body by providing our bodies
with a weapon to fight against infection and disease. The
primary function of the WBC is served
mostly after it leaves the marrow and enters the blood stream
after being carried by the RBC from
its site of formation in the marrow, to its site of labor in the
blood stream. There are five types of
white blood cells seen in blood and each has different roles to
perform.
The Neutrophil
The neutrophil, in conditions of healthand certain
disease, is usually the most common
granulocyte found in blood. The cytoplasm of the neutrophil
contains three differing types of
granules. It is these granules that result in it being termed a
granulocyte. Neutrophils generally
have segmented or hyper-segmented nuclei giving them the
appearance of being mutlinucleated.
In fact, they are not multinucleated as a thin strand of
chromatin connects each lobe of the
prominent dark purple, multilobed nucleus. At times, this
chromatin strand can be visualized by
most microscopes, when care is taken to look for it. Sometimes
however, the strand becomes
obscured by parts of the nuclei itself as a result of cell
orientation and smear technique.
The three type of granules seem in the cytoplasm of the cell
perform specific functions.
Primary granules are non-specific and contain lysosomal enzymes,
defensins, and some
lysozyme. The granules are similar to lysosomes. They stain
violet in color when prepared with
Wright’s stain or Diff Quik. The enzymes produce hydrogen
peroxide, which acts as a powerful
antibacterial agent.
Secondary granules, found in the cytoplasm of the neutrophil,
stain neutrally a light pink. They
contain collagenase, which helps the cell to move through
connective tissue, and deliver
lactoferrin, which is toxic to bacteria and fungi.
Tertiary granules have only recently been appreciated as a
granular component to granulocytes.
They are thought to produce proteins, which help the neutrophil
to stick to other cells and hence
aid the process of phagocytosis.
Neutrophils, once they arrive at an area of infection, respond
to chemicals (called chemotaxins
which are released by bacteria and nectrotic tissue cells) and
travel towards the area of highest
concentration of infection or necrotic tissue. Once they arrive
at their destination, they begin the
process of phagocytosis in which the offending cells are
engulfed and destroyed by powerful
enzymes. This process requires much energy, so the glycogen
reserves of the neutrophil are
soon depleted and the neutrophil promptly dies soon after the
phagocytotic process. When
neutrophils die, their contents spill out into the blood stream
and remnants of their enzymes
cause liquefaction of closely adjacent tissue. This results in
an accumulation of dead neutrophils,
tissue fluid and abnormal materials that is known as pus.
types but differ in the location in which they sequester for
their function.
Helper T-Lymphocytes originate in the thymus and produce long
living T-Cells which become
Killer T-Cells or K-Cells which mediate antibody dependent cell
cytotoxicity (tumor rejection).
B-Lymphocytes are localized in the corticomedullary region of
the lymph nodes and are made up
of cells of the germinal centers of the cortex in lymph nodes,
in the red pulp of the spleen, and in
available at www.lonbartoli.com and www.veterinary-hemato
logy.com
the submucosal regions of the stomach and respiratory tract.
Lymphocytes, distinguished by having a deeply staining purple
nucleus that is sometimes
eccentrically located, usually contain a relatively small amount
of cytoplasm. The small ring of
the cytoplasm contains numerous ribosomes and readily stains
blue with Wright’s Stain or
Diff-Quik. Small numbers of granules may also be noted in the
cytoplasm randomly.
Lymhpocytes increase in number as a response to viral infection.
The small lymphocyte will
approximately the same size as the normocytic RBC. The cytoplasm
is often not visible because
it is obscured by the nucleus of this cell. This cell is
definitively round under examination and
lacks “divets.” There can be variations in the size of the
lymphocyte in the k-9/f-9 with the small
type usually being the predominant type. In the small lymphocyte
the chromatin is usually so
coarse that it is masked. The medium and large forms of the
lymphocyte often appear smudged.
Lymphocytes will increase in number with restraint: physical or
chemical, and you will usually
notice a corresponding increase in PMNs.
Anemia
Anemia is defined as a below standard hematocrit (HCT). A
species specific hematocrit (1) is as
follows: Dog: 37-55, Cat: 24-45, Horse: 32-52, Porcine: 24-46,
Bovine: 24-46. There are further
variations of this data available that are further
differentiated on the basis of age and sex. The
author uses a combination of sources, which he has found through
experience to be clinically
reliable and accurate.
Most anemic conditions (except hemorrhage anemia) can be ordered
to have an etiology of
consumption, production, destruction or sequestration and
further differntiation of anemic types
are considered by ascertaining variation is size, shape,
color.
Anemias of consumption include the hemolytic anemias and those
created by disease conditions
should as DIC and parasites where platelets and other clotting
factos are consumed. Some
anemias which sequester platelets and blood to the spleen, have
also been placed in this
classification, but etiologic differentiation has been found to
be of clinical significance.
Anemias of destruction such as Autoimmune Mediate Hemolytic
Anemia (AIMHA) exist when the
body’s own antibodies destroy its own red blood cells.
Whether or not you use your own in-house clinical lab or send
your specimens out to a reference
lab, this lecture will bring you back to the basics and help you
remember that which you may have
forgotten in school. Many clinicians find this lecture and
format helpful to expand on basic
knowledge and clinically apply what they see either under
the microscope or on the lab report.
Not having adequately available time to donate towards the lab,
more clinicians are relying upon
technicians to interpret laboratory results being unsatisfied
with the time investment required to
await the return of results from distant reference labs. Clinics
and hospitals are using this
