Archives

THIS MONTH 
What is a Platelet
New Price List
Next Clin Path Club meeting
Clin Path Club Dates for 2001
Feline Pancreatitis
Feline Hyperthyroidism - Update
Total T4 - Test of Choice for Monitoring
Tail End: "Who's a Pretty Boy Then"

What is a Platelet? 
"If a kitten is a little cat
Is a mitten a little mat?
And hitten then a small size hat...?
Then what is a platelet?"

The outer membrane
Sol, gel zone
The organelles
Membrane systems

Interspersed throughout this bi-layer are specific glycoproteins. Some of these enable platelets to bind to damaged vascular endothelium and it is this process of ADHESION, which initiates platelet ACTIVATION. Following activation platelets change shape thereby exposing another novel glycoprotein (GPIIb-IIIa) which allows adjacent platelets to cross link with one another and forming a `stack’- the process of AGGREGATION.
The sol gel zone is the region of cytoplasm containing ultra-structural elements (microfilaments and microtubules) responsible for maintaining the non-activated shape and directing “shape change” and release of stored granules ( THE RELEASE REACTION), following platelet activation.

Platelets are endowed with the usual organelles such as mitochondria and lysosomes and in addition contain specific a and d granules. Their contents, released during activation, provide cofactors, including endocytosed fibrinogen), calcium and ATP which participate in platelet aggregation, recruitment and fibrin formation.
There are two important cytoplasmic membrane systems known as the “open surface – connected canalicular system” and the “dense tubular system”.

The former system is essentially an involution of, and continuous with, the outer platelet membrane, it is the site of exocytosis of a and d granule contents during the “release reaction”, and endocytosis of plasma proteins such as fibrinogen into the platelet.

The dense tubular system, composed of smooth endoplasmic reticulum, is involved in calcium sequestration and release. Increased cytosolic calcium is an essential step in the `basic platelet reaction.

Normal Platelet Function
Platelets are involved mainly in primary haemostasis. Function can be separated into four phases which occur virtually simultaneously at the site of endothelial damage: -

Adhesion
Aggregation
Release reaction
Pro-coagulant activity

Shape change exposes a previously hidden glycoprotein, GP IIb-IIIa, this is the binding site for fibrinogen expelled from a granules during the release reaction. Fibrinogen bridges form between adjacent platelets binding them into a mesh.

Pro-coagulant activity is the result of redistribution of the inner membrane phospholipid phosphatidylserine to the outer platelet membrane. This molecule subsequently acts as a catalyst bringing together coagulation factors VIII, IX and calcium (tenase complex) which activate factor X. In a similar way activated factor X interacts with prothrombin on the membrane surface (prothrombinase complex) resulting in thrombin formation. Thrombin converts fibrinogen, cross-linking platelets within the aggregate, into insoluble fibrin thus forming a stable clot.

This is the sequence of events which ensures that both primary and secondary haemostatic events are localised at the site of vascular damage and the process of repair is initiated.
To end with a cliché “diamonds are not as big as bricks” and despite their small size platelets play a vital and intricate role in haemostasis. The next time you examine a blood film and pass over the platelets in search of something more exciting, spare a thought….

Sue Beck BVMS MRCVS
Find out in the next issue what happens when platelets misbehave!

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NEW PRICE LIST
We are pleased to welcome Romain Pizzi BVSc, MSc (Wild Animal Health), MRCVS to NWL as our Exotic’s Consultant.

Regular clients should have received by now a copy of the 2002 Price List. If you have not please contact Client Services straight away. If you have received a copy, you will have noted a few changes and additions:- 

• The microbiology section now includes a Test Selection Table to help match sample with the best test code option.

 
• The Avian and Reptile Profile section has been considerably enlarged to reflect the increased interest in “exotics”. The appointment of Romain Pizzi as our consultant in this field has resulted in a marked interest in this service.

 
• The Genetics and DNA section has also been expanded. The tests in this section are being offered in association with VetGen the leading American genetic testing specialist. 

 
• The Virology and Serology section includes additions and changes. We would draw your attention to the new IgG, IgM test for Toxoplasma and the new immunofluorescent tests for Felv and FIV. Also the new range of PCR tests for blood parasites aimed at the PET scheme patients.

 
• You will note that bile acids have been removed from a number of the canine & feline profiles. This decision has been made because random bile acid tests are now considered to be of limited diagnostic value and can be misleading. The test should be done on fasting and post feeding samples or on a fasting sample as part of a liver profile. 

 
• There are a few deletions; Free T4 is no longer available. Alternatives are Total T4 or Free T4 by equilibrium dialysis. The Relaxin pregnancy test has been withdrawn because of variable results. The test is undergoing further development and is available on request but use with caution.

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CLIN PATH CLUB 
The Clin Path Club meetings are open to all veterinary surgeons and veterinary nurses.

Next Meeting: Thursday 7th March 2002 (Note Change of Date)

Venue: Swallow Hotel, Samlesbury, Preston New Road, Preston. (Leave M6 J31, follow A59 signs to Blackburn, hotel just before 1st traffic lights)

Speaker: Roger Wilkinson MA VetMB CertVD MRCVS: Clinical Pathology of Tortoises and Turtles

Case book studies: If you would like to present an interesting case please contact Jane Miller on 01253 899215 or e-mail

To book your place, request further information or a location map call Joanne Kenyon on 01253 899215 or e-mail

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CLIN PATH CLUB - Dates for 2002 
Please make a note in your diary of the forthcoming meeting on the :- 

• Thurs 9th May 2002 Simon Swift MA VetMB Cert SAC MRCVS: Clinical Cases in Cardiology - What would you do?
• Thurs 11th July 2002 To be arranged
• Thurs 12th September 2002 Dr Ian Ramsey BVSc PhD Dip ECVIM MRCVS: Recent advances in the diagnosis and treatment of Canine hyperadrenocorticism
• Thurs 14th November 2002 Dr A Coughlan BVSc Cert VA DSAS (Orth) PhD FRCVS Working up the lame dog "Tricks and Traps"

Quote “An excellent way to top up your CPD

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Feline Pancreatitis
An under diagnosed condition 
Pancreatitis is a significant disease in the cat and is recognised with increased frequency. However, due to the vague clinical signs associated with pancreatitis the condition is considered to be under diagnosed. Chronic mild pancreatitis is frequently associated with the more commonly diagnosed inflammatory bowel disease or cholangitis/cholangiohepatitis. 

Acute pancreatitis is also increasingly diagnosed in cats. Pancreatitis is considered to be a cause of Diabetes mellitus and a frequent complication in the effective treatment of the condition.

One of the contributory factors to the under diagnosis of feline pancreatitis has been the absence of an effective diagnostic test. The measurement of amylase and lipase has been the accepted approach in dogs but in cats changes in these enzymes can be misleading. Although opinions in the literature have varied as to the sensitivity of the test the determination of serum feline trypsin-like immunoreactivity is a useful diagnostic aid. A number of recent1 publications have reported that of all the procedures available the determination of fTLI is the most sensitive diagnostic aid. An abstract from one of these articles is cited below.

References 
1. Review of feline pancreatitis parts one and two.
Mansfield CS, Jones BR (2001) Journal of Feline Medicine and Surgery 2001 3, 125-132.
Abstract and copy of the above paper is available on line from www.idealibrary.com

2. Comparison of the sensitivity of different diagnostic tests for pancreatitis in cats. 
Gerhardt A, Steiner JM, Williams DA, Kramer S, Fuchs C, Janthur M, Hewicker-Trautwein M, Nolte I.  J Vet Intern Med 2001 4: 329-33 
Abstract: The objective of this study was to compare the sensitivity of different diagnostic tests for pancreatitis in cats. Twenty-one cats with confirmed pancreatitis were evaluated at the Small Animal Clinic of the School of Veterinary Medicine in Hannover, Germany, between September 1997 and January 1999. Clinical signs of affected cats were nonspecific, with 95% of the cats showing anorexia and 86% lethargy. Also, hematologic and biochemical abnormalities of affected cats were nonspecific. Serum feline trypsin-like immunoreactivity (fTLI) in these 21 cats with pancreatitis was 127.5 +/- 109.5 microg/L (mean +/- SD; range, 24-500 microg/L). Fourteen of the 21 cats with pancreatitis had complicating conditions. Their serum fTLI was 153.9 +/- 124.3 microg/L (mean +/- SD; range, 29 500 microg/L). In this study, abdominal ultrasound showed a sensitivity for pancreatitis of 24%, and abdominal computed tomography had a sensitivity of 20%. Serum fTLI had a sensitivity between 86% when a cut-off value of 49 microg/L was used (upper limit of the control range) and 33% when a cut-off value of 100 microg/L was used. We conclude that in this group of cats with pancreatitis, measurement of serum fTLI was the most sensitive diagnostic test of those evaluated. Abdominal ultrasound, however, may be a valuable diagnostic tool in some cats with pancreatitis. 

Test : TLI Feline
Code : TLIF
Sample : Serum - fasted

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Feline Hyperthyroidism - Update
It has been noted that sick cats (not hyperthyroid) may occasionally show false high Free T4 by Equilibrium Dialysis results. In these cases an additional Total T4 test should be considered. The Total T4 result would be expected to be low or low normal in a sick cat which is not hyperthyroid. These cats would also be expected to have no evidence of thyroid enlargement.

Total T4
Just to remind you that Total T4 is the test of choice for monitoring hypothyroid treatment in dogs and hyperthyroid treatment in cats. There is no benefit in using Free T4 by equilibrium dialysis for these purposes, in fact it could be missleading.

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Tail End 
"Who's a pretty boy then?" 
The secret of parrots' sex appeal has been discovered. Dr Kathryn Arnold, from the University of Glasgow has revealed how parrots and budgies have fluorescent plumage that sends a strong sexual signal to would-be partners.

It has been revealed by placing 600 dead parrots under an ultraviolet lamp and smearing the heads of live birds with sunscreen.

The UV light showed that there was nothing special about the distribution of bright red or green plumage but that the fluorescent areas were "almost always linked with areas used for courtship," bird eyes are more receptive to this effect than humans.

In an experiment in which budgies had their heads daubed with sun block, their sex appeal was reduced compared with those without. Both males and female parrots have attractive - fluorescent - plumage.