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NEWSLETTER
No 62 December 2001
Archives
THIS
MONTH
Diagnostic
Accuracy
Exotics
Specialist Consultant Appointed
Next Clin
Path Club meeting
Clin Path
Club Dates for 2001
FAQ Which
is the Best Sample for Exotics Haematology
Felv and
FIV Testing
Free
T4 Test Withdrawn
Christmas
and New Year Opening
Tail
End: "A pet that can use the internet"
Diagnostic
Accuracy
How do you select the diagnostic test which is
going to give you the information you need to make your diagnosis?
Laboratory tests such as those
for Felv, FIV, Toxoplasma etc., are generally used by clinicians to as
an aid to diagnosis. However, all diagnostic tests are fallible as a recent
paper in the Vet Record which compared in-practice tests for Felv and FIV,
pointed out. In an ideal world we would endeavour to use a “Gold Standard”
test which is considered to give rise to the least number of false results.
Unfortunately, most of these tests are not suitable for routine use in
an in-practice laboratory due to reasons of cost, complexity, skill level
or often a combination of these factors. Frequently these techniques have
been developed for use in a research environment. Routine tests are often
a compromise between sensitivity, specificity and practicality. The measure
of a good diagnostic test is based upon the ability of the test to determine
whether the disease is present or not in the circumstances in which it
is used. How is this diagnostic accuracy determined? This is a complex
subject and not one that can be answered fully in an article of this nature.
Sensitivity
and Specificity.
When selecting the most
suitable test for a particular diagnostic situation you first have to decide
if your test needs to be more sensitive or more specific. No test is 100%
specific and 100% sensitive so there are always trade-offs between these
two issues.
Sensitivity
is a measurement of the accuracy of a test in patients that truly have
the disease. It is the ratio of true positive results to the total of true
positives and false negative results.
Sensitivity = TP/(TP+FN)
In a population with a high
incidence of the disease Sensitive tests tend to have more true negatives
and more false positives. A Sensitive test is most helpful when it is negative
and so rules out the disease. In a clinical situation this could apply
when a false negative may cause problems i.e. in a treatable situation.
Specificity
is a measurement of the accuracy of a test in patients who truly do not
have the disease. It is the ratio of true negative results to the total
of true negative and false positive results.
Specificity = TN/(TN+FP)
In a population with a low incidence
of the disease Specific tests tend to have more true positives and more
false negative results. A specific test is most helpful when, positive
and rules in the disease. In a clinical situation, this could apply when
a false positive result may cause problems i.e. result in euthanasia, to
confirm a positive or disputed screening test result.
Example
This may be easier to understand
in the following analogy which compares diagnostic tests to a car alarm:-
-
If a car alarm is very Sensitive
it will sound if a car thief (true positive) breaks in or a passer by (false
positive) touches the car. Conversely if it did not sound you would be
fairly certain it was not a car thief (true negative).
-
If the car alarm is very Specific
it will only react to the car thief (true positive) breaking in but not
to the passer by (true negative) or car thief (false negative) touching
the car.
There are then there is the
question of Predictive Value, Prior Probability and Bias but that is for
an other occasion.
Reference
Hartman K. et al (2001)
Veterinary Record 149 317-320
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Exotics
Specialist Consultant Appointed
We
are pleased to welcome Romain Pizzi BVSc, MSc (Wild Animal Health), MRCVS
to NWL as our Exotic’s Consultant.
Romain Pizzi is a veterinary
surgeon with a special interest in comparative medicine, surgery, and pathology
of Exotic species, including pets such as reptiles, avians, invertebrates,
amphibians, and fish, as well as free ranging wildlife and zoo animals.
Romain was born in Port Elizabeth, South Africa, and grew up in a small
town outside Pretoria in the Transvaal province. He graduated from Onderstepoort,
the veterinary faculty of the University of Pretoria, South Africa.
After assorted veterinary
experience with non-domestic species, ranging from game capture and transport,
to African epizootic diseases, to research assistant on a project dealing
with
ostrich chicks, he came to the UK. Romain completed an MSc in Wild Animal
Health at the Institute of Zoology, London, in 2000. This included clinical
and pathology duties at London and Whipsnade zoos as part of the postgraduate
studies.
His thesis, supervised by
Andrew Cunningham, dealt with investigating the causes of mortality in
British wild birds by post-mortem examinations. This highlighted trends
in macro and histopathology findings in different native avian species
and family groups. He is currently based in private practice at the Mere
Road Veterinary Surgery in Lancashire, running a veterinary exotics (predominantly
herpetological) first opinion and referral service, as well as more routine
small animal work.
He is also involved in legal
and welfare work involving captive reptiles. Romain has delivered veterinary
papers and posters at conferences of the British Veterinary Zoological
Society (BVZS), and the Royal Entomological Society, as well as given veterinary
CPD talks. He has also written numerous short articles for herpetological
and invertebrate hobbyist magazines and societies. He belongs to a variety
of organisations including the European Association of Zoo and Wildlife
Veterinarians, the American Association of Zoo Veterinarians, the British
Veterinary Zoological Society, the Association of Reptile and Amphibian
Veterinarians, and the Veterinary Invertebrate Society, amongst others.
His current interests include:
herpetological medicine and surgery; comparative non-mammalian pathology
and haematology; ophidian physiology; field diagnostics and pathology techniques
for wildlife; husbandry, management, and reproduction of Boidae; and the
veterinary management and pathology of Theraphosidae ("tarantula") spiders.
Romain’s appointment will
enable NWL to provide an exceptional level of service to our ever increasing
number of clients with an interest in avians, reptiles and other exotics.
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CLIN
PATH CLUB
The Clin
Path Club meetings are open to all veterinary surgeons and veterinary
nurses.
Next Meeting: Thursday
15th November 2001
Venue: Myerscough
College, Bowland Suite, Bilsborough, Lancashire (The venue may change,
check back after 14th December)
Speaker: Sue Paterson
MA VetMB DVD DipECVD MRCVS: Making the most of your punch biopsies.
Case book studies: If
you would like to present an interesting case please contact Jane Miller
on 01253 899215 or mail at nwlabs@nwlabs.co.uk
To book your place, request
further information or a location
map call Joanne Kenyon on 01253 899215 mail to nwlabs@nwlabs.co.uk
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CLIN
PATH CLUB - Dates for 2002
Please make a note in your
diary of the forthcoming meeting
on the :-
Thurs 14th March
2002
Roger Wilkinson MA VetMB
CertVD MRCVS: Clinical Pathology of Tortoises and Turtles
IMPORTANT - The current speaker
programme is proving very popular. Due to a restriction on the number of
bodies we can accommodate please make sure you reserve your place early.
If you have to cancel we would appreciate a call.
Quote “An excellent way to
top up your CPD
Top
F.A.Q
Which
is the best sample for haematology in birds and reptiles?
Heparin
blood is the most flexible sample as it can be used for both haematology
and biochemistry. However EDTA gives better preservation of leucocyte morphology.
However it can cause haemolysis notably in Chelonia and ostrich. In other
species if there is sufficient blood an EDTA sample should be taken in
addition to the Heparin sample. An alternative to submitting an EDTA sample
is to make blood smears, two if possible, from fresh blood (no anti-coagulant)
if possible and submit these instead of an EDTA sample. This can be tricky
as the blood can clot very quickly making the smear useless.
Top
Felv
and FIV Testing
Should
in-practice Felv and FIV test results be checked?
In the interest of “best
practice”, any unexpected positive or negative Felv test should be confirmed
with a “Gold standard” test. In practical terms, that probably means an
Immunofluorescence test (IFT). As far as FIV is concerned, there is probably
a strong case for not doing any in-house testing unless the test confirms
your diagnosis in a sick cat. Samples should be referred to a laboratory
that offers the FIV IFT.
It has been standard practice
at NWL to check all positive Felv ELISA test results by virus isolation.
This is slow and subject to a low percentage of unsuitable samples due
to problems with sample quality. As an alternative we have been comparing
the IFT with virus isolation and the results are very promising. The only
problem is the test requires a heparin or EDTA whole blood sample (or a
blood smear). It cannot be done on a serum sample.
Special
Offer…….
For a limited period during
December we shall be offering a half price check test on your in-house
Felv and FIV test results using the IF test. If you wish to take advantage
of this offer, submit a serum and EDTA sample. Indicate the result of your
in house test and the name of the test used. In the test description area
of the request form, write tests you require together with, IF Test Offer.
This test will add an extra day to the turnaround time.
Test Code: FLVI
Test Name: Felv Immunofluorescence
test
Sample: Heparin or
EDTA whole blood or 2 blood smears
Test Code: FIVI
Test Name: FIV Immunofluorescence
test
Sample: Heparin or
EDTA whole blood or 2 blood smears
Free
T4 Test Withdrawn
Due to lack of demand the
test kit for Free T4 is to be withdrawn by the manufacturers. As a result
the test will be discontinued from the NWL list when present stocks are
exhausted.
The alternative test in dogs
is a T4 and in cats a Free T4 by Equilibrium Dialysis.
Christmas
and New Year Opening
The laboratory will only
be closed on 25th and 26th December and 1st January.
Courier collections will
operate as normal.
Top
Tail
End
"At
last, a pet that can use the internet”
BRITAIN'S best loved breed
of dog has an electronic rival with the launch of the first robot Labrador.
The cyber canine, the brainchild
of a British team of former Formula One motor racing designers, can chase
balls, climb stairs, perform tricks and acrobatics, and raise its leg to
relieve itself. It will even hurry eagerly to the front door when it expects
its master to return home. With a programmable personality, video and e-mail
links to the internet, and the strength to carry a child of five on its
back, the RoboDog is a step up from previous robotic canines.
RoboDog RS-O1 certainly walks
the walk and barks the bark, and in most other ways - its hard, shiny carbon
fibre coat, the absence of a wet nose excepted, gives its real life counterpart
a close run for realism. The price? A rather unfriendly £20,000.
Even though it does not need vaccinations, pet food, toys or castration,
it costs rather more than the £11,000 the RSPCA estimates a pedigree
costs over its lifetime.
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