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Immune-Mediated Thrombocytopenia (ITP) in Dogs
By Professor Michael Herrtage, James Warland, Andrew Kent & Julien
The Queen's Veterinary School Hospital, University of Cambridge
Thrombocytes, or platelets, are the body's first defence against bleeding.
They are tiny fragments of cells in the blood stream that are produced
by the bone marrow. These fragments constantly patrol all of the vessels
of the body in order to form a clot if any damage is caused to the vessel
wall. In order to function normally, there are usually over 175,000,000
platelets in every millilitre of your dog's blood (up to 500,000,000/ml).
The platelets form the first part of clot formation, but other factors
are necessary to form an adequate clot if any damage occurs to the blood
If there are insufficient numbers of platelets present, the blood is not
able to quickly form a normal clot. In a condition called immune mediated
thrombocytopenia, the dog's own immune system attacks and destroys these
Although in most cases, thrombocytopenia is the only problem, in some
cases ITP will be part of a wider autoimmune condition, with other organs
affected. Examples of this include Evan's Syndrome, where the body attacks
both the platelets and red blood cells (causing anaemia) or Systemic Lupus
Erythematosus (SLE), where the body attacks multiple tissues.
Causes and Diagnostic Tests
ITP is caused by an autoimmune attack against the dog's own platelets,
and usually the initial cause of this is unknown. It can be a primary
problem or a secondary problem, triggered by other diseases. In the case
of a dog with abnormal bleeding, your vet will need to run some tests
to establish the cause. Blood tests will show a low platelet count (thrombocytopenia),
however, it should be noted that ITP is not the only cause of thrombocytopenia.
Depending on your dog's previous medical history and their findings, your
vet may choose to do further tests to look for an underlying cause of
the thrombocytopenia. ITP can be caused by various infections, including
viral and bacterial infections. The most important type of infection to
cause thrombocytopenia in the UK is Ehrlichia, which is spread by ticks,
and your vet will be able to test for this if infection is possible. Your
vet may also perform other tests, such as X-rays and ultrasound of your
dog to look for other causes of thrombocytopenia. Some drug treatments,
particularly antibiotics and anti-inflammatory drugs, can cause thrombocytopenia.
Unfortunately, ITP is diagnosed by ruling out other potential causes of
low platelet numbers.
It is important to inform your vet if your dog has travelled outside the
UK, as various infections that are not native to the UK can cause thrombocytopenia
and it may be appropriate to test for these as well.
In dogs with ITP the most common clinical signs are associated with
bleeding. Because clots are constantly being formed to prevent bleeding,
even when no obvious trauma has occurred, dogs usually show signs of bleeding
even without injuring themselves. Nosebleeds, bruising of the skin or
gums, or petechiae (small red spotted rash caused by leaking capillaries)
are common signs of ITP. Some dogs will have bleeding into their intestines,
which cannot be seen initially, but leads to black, tar-like faeces (melaena).
Some dogs will have more unusual sites of bleeding that can lead to other
problems, such as bleeding in the brain or the eye.
Bleeding from the gums in an Irish Wolfhound with ITP
Petechial haemorrhages on the penis of an Old English Sheepdog with
Small petechial haemorrhages in the skin of a Springer Spaniel with
In ITP, the treatment is first aimed at decreasing the overactive
immune system which causes this platelet reduction. The drugs used to
decrease the overactivity of the immune system are called immunosuppressive
The main type of immunosuppressive drugs is corticosteroids, of which
prednisolone remains the most frequently prescribed. Doses of prednisolone
vary markedly between patients but high doses are generally used at the
beginning of the treatment. Like any medication, prednisolone can be associated
with side effects (e.g. increased drinking and urination, increased appetite,
weakness, or rarely vomiting or diarrhoea). These side effects are by
far less frequent than in human patients, allowing some canine patients
to be treated only with prednisolone for a prolonged period.
If prednisolone alone does not control the clinical signs or if side effects
are noticed, your own vet may also prescribe other immunosuppressive drugs
(e.g. azathioprine, cyclosporine).
If the platelets level is critically low and bleeding had occurred, your
veterinarian may suggest transfusion of fresh canine blood or other blood
components. As in human patients, transfusion reactions may occur and
your dog will have to be closely monitored during this transfusion. In
dogs, transfusion reactions are rare after the first transfusion. However,
if your dog has already received a blood transfusion, the risk for adverse
reactions increases markedly. It is important to mention previous transfusions
to your own veterinarian.
The spleen is the principal site of destruction of platelets during ITP.
A surgery to remove the spleen has been advocated in severe cases of ITP
which failed to respond to medical treatment. We rarely recommend this
surgery in our hospital but this must be discussed with your own veterinarian.
If ITP is severe enough, hospitalisation in a referral hospital may be
needed. In a referral hospital access to unusual medications, including
human medication may be facilitated (e.g. intravenous human immunoglobulin,
vincristine, mycophenolate mofetil).
ITP is considered to be idiopathic or primary when no underlying
cause is found. Secondary ITP occurs when an underlying cause is identified
which may include:
" Rickettsial infections e.g. Ehrlichia canis, Anaplasma phagocytophilum
" Drugs e.g. trimethoprim/sulfadiazine, cephalosporin
Any breed, sex or age of dog can be affected by ITP. It seems to be more
common in middle aged, female dogs, particularly Cocker Spaniels, Old
English Sheepdogs, Miniature and Toy Poodles.
People often worry that the ITP has been triggered by recent vaccination,
as this link has been established in humans (although is exceedingly rare).
In dogs it has not been proven that any vaccination causes ITP, and if
it does occur it is also likely to be a rare event. It is very important
to remember that many of the diseases your dog is vaccinated against are
far more dangerous and common than the rare side effects associated with
vaccination. If you are concerned about side effects of vaccination in
dogs please discuss this with your veterinarian.
In a study of dogs in the USA, 5.2% of dogs admitted to a specialist
veterinary hospital were found to have reduced numbers of platelets. Of
these dogs 5% were diagnosed with ITP meaning it was the cause of 0.26%
of hospital admissions.
This suggests that it is still a fairly uncommon disease, however it
was the most likely cause of developing a very low platelet count (<
The majority (>70%) of dogs with IMT (Immune-Mediated Thrombocytopenia)
will show significant improvement with prednisolone alone or in combination
with other immunosuppressive drugs in less than a week. After stabilisation
with treatment, the doses are usually slowly tapered down while monitoring
closely the platelet value.
During this progressive reduction in dose, there is a risk of recurrence
of the clinical signs which may be observed in around 25% of the patients.
Following recurrence, treatment should be reinstituted at a higher dosage
and your veterinarian will discuss further treatment options.
Unfortunately, despite appropriate treatment around 10 to 15% of dogs
with ITP can die or are euthanised at the beginning of the disease or
after recurrence of their signs. This is mainly observed with severe disease
associated with complications like coagulation disorders or severe gastro-intestinal
bleeding. Rapid institution of the treatment and close monitoring during
hospitalisation have been associated with reduced risk in dogs with ITP.
If you are owned by a dog or other pet with ITP and wish to use the
services of the ITP Support Association, do feel free to join our Association
or make a donation to help us with our work.
There is no state funding for ITP research, and this charity cannot fund
ITP research without help from those who have an interest in finding a
cure, whether it be patient, family member, friend or pet owner.
Association's Veterinary Advisor
Andrew Kent BVSc DipECVIM-CA MRCVS
European Veterinary Specialist in Small Animal Internal Medicine
Willows Referral Service
West Midlands B90 4NH
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study of 871 dogs with thrombocytopenia." Veterinary Record. 2009;
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survey of thrombocytopaenia in dogs: A report on 987 cases." Veterinary
Clinical Pathology 1991; 20: 38-43.
- Huang A.A., Moore G.E., and Scott-Moncrieff J.C., "Idiopathic
Immune-Mediated Thrombocytopenia and Recent Vaccination in Dogs,"
Journal of Veterinary Internal Medicine 26, No. 1, 142-148.
- Laurel J. and Gershwin D.V.M., "Autoimmune Diseases in Small
Animals," Veterinary Clinics of NA: Small Animal Practice 40, No.
- O'Marra S.K., Delaforcade A.M., and Shaw S.P., "Treatment and
Predictors of Outcome in Dogs with Immune-Mediated Thrombocytopenia."
Journal of the American Veterinary Medical Association 238, No. 3: 346-352.
- Putsche J.C., Kohn B., "Primary immune-mediated thrombocytopenia
in 30 dogs (1997-2003)." Journal of the American Animal Hospital
Association, 2008, 44, 250-257.