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LABORATORY
WINTER 2014 ISSUE
EQUINE MATTERS
14
The test strip is dipped into the urine; this
identifies any evidence of protein, blood,
haemoglobin and the pH of the urine.
Dipstick analysis
The urine sample is mixed well and a
small amount of sample is then spun down
to concentrate any cells which may be
present. This is placed on a microscope
slide and examined. The slide is checked
for the presence of RBC, WBC, bacteria,
and crystals. Calcium carbonate crystals
are commonly seen in normal horse urine.
Sediment
Different tubes for collecting blood samples
Top colour
Anticoagulant
None
EDTA
Heparin
Fluoride oxalate
Citrate
Test
Biochemistry
Haematology
Biochemistry
(quicker to use as do
not need to wait for
sample to clot)
Glucose
Coagulation
studies
Fibrinogen
Red
Urine colour
Yellow
Normal
Red
Blood in urine
Purple
Green
Grey
Blue
l
Packed cell volume (PCV)
- is the
percentage of blood made up of red
blood cells. Increased PCV can
be due to dehydration. Decreased
PCV is commonly seen in anaemia or
blood loss.
l
White blood cell differential
- can be
done manually by preparing a blood
smear. A small drop of blood is placed
onto a microscope slide and spread
across the slide. The slide is allowed to
dry and then stained. Once the stained
slide is dry, it is then examined under
the microscope at a high power
magnification.
l
‘wet’ analyser
- where liquid reagents
are added to samples and the
chemical reaction measured;
l
‘dry’ analysers
- where individual tests
are carried out on slides and lights are
passed through and the intensity of the
light is measured.
Haematology
This is usually carried out by a haematology
analyser which has set reference ranges for
each component so there can be variation in
results depending on the type of analyser
used. The haematology analyser looks at the
red and white blood cell counts. The white
blood cell count is separated out into the
individual white cells; this is known as the
differential count.
Some tests can be carried out
individually
Biochemistry
Is carried out in automated machines which
are either:
Common tests performed in equine practice
on biochemistry analysers are muscle
enzymes (CK, AST) commonly elevated in
azoturia ('tying up'), liver and kidney function
and assessment of proteins.
Urine
Urinalysis is the examination of urine.
This involves:
l
specific gravity (SG)
- measure of the
density of urine;
l
biochemistry tests
- dipstick analysis;
l
sediment
- microscopy examination.
Ideally the sample should be a free-flow
sample collected mid-stream.
The sample is initially examined visually in
the pot - normal horse urine is yellow and
may be either cloudy or clear in appearance.
Brown red/black
Muscle damage
Faecal analysis
The most common test on faeces is a worm
egg count - this is carried out by faecal
flotation using salt solution and examined
on the microscope using a McMaster slide
(counting chamber). The number of eggs
detected correlates with individual worm
burden.
Other tests
available
l
Hairs plucks
- for 'ringworm' culture
and identification of ectoparasites such
as lice.
l
Sellotape preparations
- used to
identify pinworm infestations in the
peri-anal region.
l
Skin scrapings
- for identification of
mites such as Chorioptes (leg mites).
Hair and skin sampling
Bacteriology
Hair samples are routinely examined
as skin conditions are common.
l
WBC
- either with commercial analyser
or microscopy;
l
Biochemistry
- looking at proteins to
indicate an inflammatory response.
Visual examination of the samples is also
performed; normal samples should be pale
yellow and clear.
Some practices have the facilities to carry out
bacteriological culture. Samples or swabs
are placed onto selective media in petri
dishes and incubated to see if bacteria grow.
The bacteria are then examined by making
a smear on a slide, staining and examining
on high power under the microscope.
Synovial fluid and peritoneal
fluid analysis
Commonly obtained for diagnosis of
septic joints and peritonitis - the tests
routinely carried out on the samples are: