Diagnostic Techniques
LAT Chapter 10
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Chapter 10
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To Make A Diagnosis
Chapter 10
• Diagnosis responsibility of veterinarian.
 Diagnostic tests may be performed by a technician.
• Diagnostic techniques, history, clinical examination,
other information considered.
and
• Also used to define or establish health status of a
clinically normal animal.
• Diagnostic techniques: radiography, anatomical
pathology, necropsy, microscopic examination of tissue
sections, clinical pathology, microbiology, hematology,
blood chemistry, immunoserology, parasitology and
urinalysis
Anatomical Pathology
Chapter 10
• Study of structure of diseased tissues
 Gross pathology performed at necropsy.
 Perform necropsies as soon after death as possible.
 Animals that cannot be examined immediately should be
refrigerated, but not frozen, to slow the process of decomposition.
• Proper protective clothing must always be worn while
conducting a necropsy.
• Good necropsy has consistent, thorough, routine method
for examining the entire carcass.
 Examine exterior of animal. Open abdomen and each internal
organ is examined in a specific order. Next the thorax is opened,
and heart and lungs are observed.
 Make a precise record of each tissue collected and label each
container accurately with the types of tissues, date of collection
and name of investigator.
Necropsy
Chapter 10
• Collected tissues are preserved by
placing
them in a solution of 10-percent buffered formalin.
 Stops all tissue decomposition and “fixes” the tissue to preserve its
anatomical structure.
• Place remains in leak proof bag and barrel.
 If radioactive or infectious, store and dispose of separately.
 Mark containers with hazardous material involved.
• Once fixed, slices of tissue are cut and placed in trays.
 Next they are treated with a number of chemicals, and then
embedded in paraffin.
 Slices mounted on slides and stained with dyes.
 Procedure is referred to as histopathology (histo = tissue).
Clinical Pathology
Chapter 10
• Analysis of blood, urine, feces,
tissues, and exudates
• Diagnostic microbiology to isolate and identify
microorganisms, interpret culture results, and perform
antibiotic sensitivity tests
• Sterile swabs of various types are used for collection of
cultures from the area that is thought to be infected.
 Throat swabs - don’t touch lips, tongue, or other oral surfaces.
• When culturing wounds or abscesses, obtain sample
from the edge, or wall, of the lesion.
• Fresh feces for microbiological examination should be
collected in a clean container.
 If feces not available, a rectal swab is acceptable but less ideal.
Bacterial Culture
Chapter 10
• Prevent drying of the sample or swab.
 Ampule at bottom of culture container is crushed to release fluid
transport medium to keep bacteria alive for 24 hrs.
• Sample is inoculated for culture and identification.
 Individual colonies are picked and grown as a pure culture.
 Tentative ID made based on colony shape and staining.
 Definitive ID requires biochemical, serological, and various tests.
• Antibiotic sensitivity
 Organisms inoculated over the surface of petri dish then several
small disks containing various antibiotics placed on surface.
 If sensitive to a particular antibiotic, growth will be inhibited
around that particular sensitivity disk.
 Supplies information for prescribing proper antibacterial therapy.
Hematology
Chapter 10
• Blood = erythrocytes (red blood cells),
leukocytes (white blood cells), platelets, and plasma
• Total blood volume = ~ 6–8% of body weight.
• Blood cell structures and normal ratios provides
information to evaluate health status.
• Reptiles, amphibians, and birds all have nucleated
erythrocytes.
• Rabbits and guinea pigs have neutrophils with red
staining granules in the cytoplasm that make these cells
appear more like the eosinophils of dogs.
• Some guinea pig lymphocytes also contain large, redstaining granules called Kurloff bodies.
Blood Collection
Chapter 10
• Red blood cells ruptured (hemolysis)
during collection by pulling too hard during aspiration, or
by forcing blood in a syringe through a needle.
 Can result in inaccurate values for clinical chemistry tests.
 Insert the needle bevel up to ensure smooth entry into the vein.
 Syringe plunger pressure just sufficient to pull blood in.
 Needle held firmly while attaching vacuum vial to prevent the
needle from pulling out or being pushed through vein.
• Large animals - collect from veins on legs or from jugular.
• Mice / rats – collect small amount of blood from the tail
vein, heart or retroorbital.
• Rabbits - collect from the vessels in the ear.
Blood Collection
Chapter 10
Serum & Plasma
Chapter 10
• EDTA, sodium citrate or heparin prevent clotting, which
allows whole blood to be separated into plasma and the
red cells, white cells and platelets.
• Whole blood will separate into clotted and a liquid fraction.
 Some tests require whole blood, others require serum or plasma.
• Red (orange) stopper indicates no anticoagulant.
 Used to collect blood that is going to be allowed to clot.
• Purple (lavender) stopper indicates EDTA.
 Prevents clotting and allow the collection of plasma.
• Green stopper indicates heparin.
• Centrifuge spins tube very rapidly and forces the cells or
clot to bottom, separating liquid from cellular fractions.
 The liquid (serum or plasma) can then be removed.
Blood Diagnostic Tests
Chapter 10
1.Packed Cell Volume (PCV) = hematocrit, is a measure of
the % of cells vs. liquid in the sample.
2. Differential Leukocyte Count is a count of different types
of leukocytes in a drop of whole blood.
3. Total Red and White Cell Counts
• When a diagnostic laboratory receives a request to
perform a Complete Blood Count (CBC) on a blood
sample, the lab will do all of the tests listed above, plus
several more not mentioned here.
• Clinical chemistry tests help to determine that the kidney,
liver and other organs are functioning normally.
Chapter 10
Blood Chemistry
Chapter 10
• Accuracy of tests depends on method of collecting and
transporting specimen.
 If whole blood or plasma is required, sample is immediately
mixed gently with a anticoagulant.
 If serum is required, the sample is allowed to clot.
• Proper withdrawal and submission procedures =>
uniform, representative specimens.
• Tests for renal (kidney) function include analysis for blood
urea nitrogen (BUN) and creatinine.
 Waste products produced during normal body metabolism.
 These waste products are eliminated mainly by the kidneys, and
elevated blood levels of either one usually indicates an
abnormality in the urinary system.
Chapter 10
Blood Chemistry (continued)
Chapter 10
• Chemical tests of liver function include metabolic tests,
excretion tests, and serum enzyme tests.
 Some substances formed in the liver are bile pigments, albumin,
fibrinogen, prothrombin, and cholesterol.
• Excretion tests involve intravenous injection of dyes.
 At a standard time after injection, blood level of dye is measured
and excretion rate calculated.
• Enzymes in high concentration within the cells of the liver.
 When damaged, enzymes are released into the blood stream.
• Serum ion levels important in disease diagnosis and
postsurgical treatment.
 If uncorrected, severe illness or death may result.
 sodium (Na), potassium (K), magnesium (Mg), calcium (Ca),
phosphorus (HPO4), and chloride (Cl)
Chapter 10
Immunoserology
Chapter 10
• Disease agents act as antigens (immune system
stimulators) => protein molecules called antibodies.
• Antibodies in the serum indicate either an active
infection, or exposure to disease.
• Serum antibody levels = antibody titer.
• Techniques to measure antigen-antibody reactions
 complement fixation, fluorescent antibody precipitation,
hemagglutination, and ELISA
• Consecutive samples determine if antibody level is rising,
falling, or remaining constant.
 An indication of the immune competence of the host, as well as
approximate stage of the disease.
Chapter 10
Immunoserology (continued)
Chapter 10
• Viruses differ from bacteria mainly by being intracellular
and requiring living cells in which to grow.
 Solutions containing cells known to support viral growth are used.
• Once inoculated cells in the culture become infected,
damaged or killed in characteristic patterns.
• Testing tissues for the presence of DNA from specific
organisms is a means of identifying a disease.
• A procedure called the polymerase chain reaction (PCR)
has made it possible to detect very small numbers of
organisms by artificially increasing (amplifying) the DNA
they contain.
Parasitology
Chapter 10
• Therapy and prevention depend on accurate ID of a
parasite or parasite ova.
• To detect helminth (worm) infections, fecal examination
for ova is performed.
• Pinworms (Syphacia spp.), lay their eggs on the exterior
of animal around the anus.
• Heartworm infestation of dogs and cats is diagnosed by
microscopic examination of the blood for microfilaria
(immature larval forms).
• External parasites, especially mites, may be identified by
microscopic examination of the fur or by skin scrapings.
University of Illinois Department of Entomology:
http://www.life.uiuc.edu/entomology
Flea Lifecycle
Chapter 10
Roundworm Ova
Chapter 10
Pinworm Egg
Chapter 10
Syphacia species
Pinworm Eggs
Chapter 10
In The Uterus of Mature Adult 
Male Adult Pinworm
Chapter 10
Syphacia mesocriceti
“Grain Beetle”
Chapter 10
Found in infested rodent feed bags
Hamster Skin Mite (lateral view)
Chapter 10
Demodex aurate.
Hamster Skin Mite (ventral view)
Chapter 10
Demodex aurate.
Psoregates Mange Mite (ventral view)
Chapter 10
Isolated from Non-Human Primate
Urine Examination
Chapter 10
• Physical, chemical tests + microscopic exam of sediment
 culture and antibiotic sensitivity testing of bacteria isolated from
urine for diagnosing and treating bacterial infections
• pH (acid or alkaline), specific gravity, color, and volume
• Chemical tests detect mainly proteins, carbohydrates,
electrolytes, pigments, and hormones.
• Urine sediment examination identifies cells, renal tubular
casts, and crystals.
 Location of a disease in the urinary tract determined through
examination of the urinary sediment.
• Important collection consideration:
 Specimen must be collected in a clean, dry container.
Diagnostic Imaging
Chapter 10
• Bone absorbs X-rays, air absorbs very few X-rays.
 The film directly beneath the bone appears white.
 Film placed under the lungs appears dark or black.
• Movement will cause blurring of the image and make
interpretation of the image more difficult.
• Fluoroscope - X-rays of moving objects
 X-rays are ionizing radiation.
 Proper shielding worn by
personnel at all times.
• Computerized Axial Tomography
• Positron Emission Tomography
• Magnetic Resonance Imaging
• Ultrasound scanning
Summary
Chapter 10
•
Effective treatment can be initiated sooner if diagnostic
results can be made quickly available to the clinician
treating a disease outbreak.
• The diagnostic techniques discussed above are equally
important in determining the true health status of normalappearing animals, since subclinical infections can have
devastating effects on research results.
• It is through the combined use of these techniques,
coupled with clinical examination and daily observations
by laboratory animal technicians, that the health status of
both individual animals and entire colonies can be
accurately defined.
Summary (continued)
Chapter 10
Additional Reading
Chapter 10
1. McCurnin, D.M. Clinical Textbook for Veterinary
Technicians. W.B. Sanders, Philadelphia, PA, 1994.
2. Pratt, P.W. Laboratory Procedures for Veterinary
Technicians. Mosby, St. Louis, MO, 1996.
3. Sharp, P.E. and La Regina, M.C. The Laboratory Rat.
CRC Press, New York, NY, 1998.