Changes

[[Platelet|Platelets]] (or thrombocytes) are responsible for primary haemostasis by the formation of a temporary platelet plug that initially seals any breach to a blood vessel wall.  These breaches are then sealed more completely by the formation of a fibrin clot induced by the coagulation factor cascade.   

[[Platelet|Platelets]] (or thrombocytes) are responsible for primary haemostasis by the formation of a temporary platelet plug that initially seals any breach to a blood vessel wall.  These breaches are then sealed more completely by the formation of a fibrin clot induced by the coagulation factor cascade.   

===Terminology===

===Terminology===

*'''Thrombocytopaenia''' refers to low absolute numbers of platelets. [[Immune Mediated Thrombocytopaenia|Immune-mediated thrombocytopaenia]] (ITP) is one common cause of thrombocytopaenia and this may be a primary or secondary disease.   

*'''Thrombocytopaenia''' refers to low absolute numbers of platelets. Infections, neoplasia and [[Immune Mediated Thrombocytopaenia|immune-mediated thrombocytopaenia]] (ITP) are common causes of thrombocytopaenia, which is frequently a secondary disease.   

*'''Thrombocytopathia''' refers to platelets that are unable to function adequately.

*'''Thrombocytopathia''' refers to platelets that are unable to function adequately.

*'''Thrombocytosis''' refers to an increase in the blood platelet concentration above the normal level.

*'''Thrombocytosis''' refers to an increase in the blood platelet concentration above the normal level.

==Thrombocytopaenia==

==Thrombocytopaenia==

Thrombocytopaenia is a common haematological abnormality as platelet numbers are subject to fluctuation in a number of diseases. Care should be taken, however to ensure that this finding is not caused by an artefact of sampling where platelet clumps have formed.  The normal blood platelet concentration of the dog is 175-500x10^9 but clinical disease is not usually observed until this level falls below 50x10^9 and spontaneous haemorrhage is observed only when the level falls below 20x10^9. Reductions in platelet numbers may be caused by a failure to produce adequate amounts in the bone marrow during [[Thrombopoiesis|megakaryopoiesis]], or an increased destruction of existing platelets or sequestration of platelets outside of the circulation.   

Thrombocytopaenia is a common haematological abnormality as platelet numbers are subject to fluctuation in a number of diseases. Care should be taken, however to ensure that this finding is not caused by an artefact of sampling where platelet clumps have formed.  The normal blood platelet concentration of the dog is 175-500x10^9; a tendency to bleed following an insult such as venepuncture can be observed if levels fall below 50x10^9 and spontaneous haemorrhage is observed when levels fall below 30x10^9. Acute thrombocytopenia is more likley to give rise to clinical signs than more chronically developed low platelet numbers.

 

Reductions in platelet numbers may be caused by a failure to produce adequate amounts in the bone marrow during [[Thrombopoiesis|megakaryopoiesis]], or an increased destruction of existing platelets or sequestration of platelets outside of the circulation.   

===Causes of bone marrow suppression===

===Causes of bone marrow suppression===

===Causes of increased platelet destruction===

===Causes of increased platelet destruction===

*'''Infectious diseases''' that cause destruction of platelets include [[Bovine Viral Diarrhoea Virus|bovine viral diarrhoea (BVD)]], [[Classical Swine Fever|classical swine fever]] and [[Infectious Canine Hepatitis|infectious canine hepatitis]].  The parasites [[Ehrlichia platys|''Anaplasma platys'']], [[Ehrlichia phagocytophila|''Anaplasma phagocytophilum'']] and ''[[Ehrlichia canis]]'' may also cause infectious thrombocytopaenia.  Any severe bacterial infection, including those caused by [[:Category:Staphylococcus species|''Staphylococci'']] and the Gram negative bacteria that produce endotoxins (e.g. [[:Category:Pseudomonas and Burkholderia species|''Pseudomonas sp.'']] or [[Salmonella|''Salmonella sp.'']]) may also result in the destruction of platelets.

*'''Infectious diseases''' that cause destruction of platelets include [[Bovine Viral Diarrhoea Virus|bovine viral diarrhoea (BVD)]], [[Classical Swine Fever|classical swine fever]] and [[Infectious Canine Hepatitis|infectious canine hepatitis]].  The parasites [[Ehrlichia platys|''Anaplasma platys'']], [[Ehrlichia phagocytophila|''Anaplasma phagocytophilum'']] and ''[[Ehrlichia canis]]'' may also cause infectious thrombocytopaenia.  Any severe bacterial infection, including those caused by [[:Category:Staphylococcus species|''Staphylococci'']] and the Gram negative bacteria that produce endotoxins (e.g. [[:Category:Pseudomonas and Burkholderia species|''Pseudomonas sp.'']] or [[Salmonella|''Salmonella sp.'']]) may also result in the destruction of platelets.

===Causes of platelet sequestration===

===Causes of platelet sequestration===

===Artefactual or spurious thrombocytopaenia===

===Artefactual or spurious thrombocytopaenia===

*'''Cavalier King Charles spaniels''' have a genetic abnormality which produces a small number of giant platelets (macrothrombocytes) in the circulation with a corresponding reduction in free platelets; they do not suffer from bleeding disorders as they maintain a similar total platelet mass as do dogs of other breeds. Automated blood counts will include the macrothrombocytes in the white or red cell count and the apparent thrombocytopenia will be exaggerated.  

*'''Cavalier King Charles spaniels''' have a genetic abnormality which produces a small number of giant platelets (macrothrombocytes) in the circulation with a corresponding reduction in free platelets; they do not suffer from bleeding disorders as they maintain a similar total platelet mass as do dogs of other breeds. Automated blood counts will include the macrothrombocytes in the white or red cell count and the apparent thrombocytopenia will be exaggerated.  

*If venepuncture is traumatic, '''platelet clumps''' may form and these will not be counted by automated machines.  The presence of clumps can be investigated by making a blood smear and examining the feathered edge for large agglomerations of platelets.

*If venepuncture is traumatic (using small viens with excessive suction or patient agitation) '''platelet clumps''' may form and these will not be counted by automated machines.  The presence of clumps can be investigated by making a blood smear and examining the feathered edge for large agglomerations of platelets. Time, temperature and contact with glass can also cause clumping of platelets once the sample has been taken.

==Thrombocytopathia==

==Thrombocytopathia==

*'''Splenic contraction''' which pushes sequestered platelets into the circulation.  This phenomenon is especially marked in '''horses''' which have a muscular splenic capsule.   

*'''Splenic contraction''' which pushes sequestered platelets into the circulation.  This phenomenon is especially marked in '''horses''' which have a muscular splenic capsule.   

*'''Splenectomy''' prevents the sequestration of platelets in the spleen, resulting in consistently increased levels of platelets.

*'''Splenectomy''' prevents the sequestration of platelets in the spleen, resulting in consistently increased levels of platelets.

*As part of a response to [[Anaemia - Introduction|anaemia]] a '''reactive thrombocytosis''' is often documented and this may precede signs of regeneration.

*As part of a response to [[Regenerative and Non-Regenerative Anaemias|anaemia]] a '''reactive thrombocytosis''' is often documented and this may precede signs of regeneration.

Pathological

Pathological

==Clinical Significance==

==Clinical Significance==

Other than essential thrombocythaemia, thrombocytosis has no clinical importance except as an indicator of another disease process.  Thrombocytopaenia and thrombocytopathia both result in reductions in the effectiveness of primary haemostasis, producing bleeding disorders.  Since bleeding points are usually sealed by a fibrin clot, disorders of primary haemostasis tend to be less severe than those caused by deficiencies of the coagulation factors.  Common signs of a disorder of primary haemostasis include:

Other than essential thrombocythaemia, thrombocytosis has no clinical importance except as an indicator of another disease process.  Thrombocytopaenia and thrombocytopathia both result in reductions in the effectiveness of primary haemostasis, producing bleeding disorders.  Since bleeding points are usually sealed by a fibrin clot, disorders of primary haemostasis tend to be less severe than those caused by deficiencies of the coagulation factors.  Common signs of a disorder of primary haemostasis include:

*'''Petechial''' or '''ecchymotic''' haemorrhages on the skin or mucous membranes.

*Petechial or ecchymotic [[Haemorrhage|haemorrhages]] on the skin or mucous membranes.

*'''Haemorrhages from the mucous membranes''', producing haematuria, haematochezia, haematemesis, haemoptysis and melaena.

*[[Haemorrhage|Haemorrhages]] from the mucous membranes, producing haematuria, haematochezia, haematemesis, haemoptysis and melaena.

*'''[[Anaemia - Introduction|Anaemia]]''' with reactive [[Neutrophilia|neutrophilia]] and [[Monocytosis|monocytosis]] if the haemorrhage is severe.

*[[Regenerative and Non-Regenerative Anaemias|Anaemia]] with a reactive [[Neutrophilia|neutrophilia]] and [[Monocytosis|monocytosis]] if the haemorrhage is severe.

 

 

 

 

Severe platelet deficiencies may be managed with transfusions of whole blood or, in the USA, with transfusions of platelet cryoprecipitate. With both techniques however, it is likely that the transfused platelets have only a short half life in the recipient.

[http://www.cabdirect.org/search.html?q=title%3A%28thrombocytosis%29&fq=sc%3A%22ve%22 Thrombocytosis publications]

[[Category:Haemorrhagic Diseases]]

[[Category:Haemorrhagic Diseases]]

[[Category:To Do - James]][[Category:Haematology Changes]][[Category:To Do - Review]]

[[Category:Haematology Changes]]

[[Category:Lymphoreticular and Haematopoietic Diseases - Dog]]

[[Category:Cardiology Section]]