Hemostatic disorders occur in all pathways of hemostasis and can be inherited or acquired. They are usually recognized clinically by excessive hemorrhage. History, signalment and clinical signs can guide a clinician as to the likely underlying disorder. For instance, disorders of primary hemostasis are characterized by mucosal hemorrhage and small bleeds (petechiae) when there is thrombocytopenia or thrombopathia. Disorders of secondary hemostasis result in larger bleeds (hematomas) and intracavity bleeding. Thus, a thorough history (travel, exposure to toxins, drug treatment) and clinical examination (assessment of the skin and all mucosal surfaces for hemorrhage) are mandatory in bleeding animals.  Ancillary diagnostic testing (e.g. hemograms, biochemical panels, radiographic and ultrasonographic examination) may be indicated in individual animals, particularly those that are sick, to confirm or rule out underlying disease as a cause for the hemostatic disorder. Acquired disorders are by far the most common, particularly thrombocytopenia. Inherited disorders predisposing animals to thrombosis (deficiencies in anticoagulants, defective fibrinolysis) are rare and it is difficult to recognize thrombosis clinically, leading to under-recognition of acquired prothrombotic diseases.

In this section, we have split up hemostastic disorders based on physiology, although some disorders, which encompass multiple aspects of hemostasis, are placed as separate categories:

Hemostatic disorders can also be inherited or acquired.

Inherited disorders

Inherited disorders of hemostasis should be suspected in an animal presenting with bleeding symptoms at a young age, specially those that are clinically healthy, are of a predisposed breed, demonstrate recurrent bleeding episodes, or have a known family history. Some animals with mild inherited bleeding disorders may only be diagnosed when they are adults as their bleeding symptoms are mild or instigated by trauma or surgical procedures. Therefore, an inherited bleeding disease should not be excluded in adults. It is imperative to obtain a good history from clients of an adult bleeding animal in order to ascertain at what age the hemorrhage was first noticed, if it is recurrent and if it is precipitated by trauma (even the kind of trauma sustained from chewing a bone or rawhide). Recurrent hemorrhage (especially that separated by days, weeks or months or that is precipitated by trauma of some kind) is a good indicator of an inherited bleeding disorder.

Inherited disorders of hemostasis are most commonly recognized in dogs. They are rare in horses and cattle. They do occur in cats but are less frequently as cats do not commonly show signs of hemorrhage (perhaps due to their small size and relaxed lifestyles), unless subjected to surgical procedures, such as declawing or neutering.

The most common inherited diseases are von Willebrand disease (primary hemostasis), which is the most common inherited disorder of hemostasis, and hemophilia A (factor VIII deficiency, secondary hemostasis). Inherited disorders of the blood vessel wall, platelet number, platelet function, and inhibitors are quite rare.

Acquired disorders

Acquired disorders of hemostasis can occur in an animal of any age, but are more common in older animals due to underlying diseases. Animals presenting with clinical signs of hemorrhage should be thoroughly examined for underlying diseases (e.g. hemogram, biochemistry panel, radiographic and ultrasonographic examination) that may have precipitated the hemorrhage. This is particularly true for older animals. Also since drugs may cause or exacerbate a bleeding tendency (e.g. aspirin), a thorough drug history should be taken from clients with a bleeding animal.

The most common hemostatic abnormalities encountered in private veterinary practice are acquired disorders, in particular immune-mediated thrombocytopenia, anticoagulant rodenticide toxicosis, and metabolic diseases that affect hemostasis (such as liver disease) or induce disseminated intravascular coagulation (DIC; such as severe inflammation, sepsis, cancer).

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