Primary hemostasis disorders Flashcards
Describe the steps of the primary hemostasis mechanism
Primary hemostasis (vascular/platelet phase)
- step 1: vasoconstriction triggered by vessel injury
- step 2: platelets adhere to exposed vascular sub-endothelium
- this is facilitated by von Willebrand factor which is a large glycoprotein that binds to both collagen and a platelet receptor
- step 3: more platelets adhere to original platelets (primary aggregation)
- step 4: platelets change shape and release substances that promote vasoconstriction and activate more platelets (release reaction)
- step 5: more and more platelets adhere to the site (secondary aggregation) until the leak in the vessel is sealed with a soft plug
- step 6: this fragile plug must be reinforced with fibrin, which is activated via secondary hemostasis
How can you group disorders of primary hemostasis
Disorders of primary hemostasis can be grouped into four main categories:
- thrombocytopenia (decreased platelet number)
- thrombocytopathy (impaired platelet function)
- vascular disorders (e.g., collagen deficiency diseases)
- VWF deficiency (rare in cats)
What can you conclude when observing clumping of platelets on a blood smear
Clumping of platelets usually indicates that there are sufficient numbers present to prevent bleeding (> 50*10^9/L)
Cat’s platelets are hyper-coagulable
What is the typical presentation for thrombocytopenia
Significant decreases in platelet numbers typically present as a disorder of hemostasis
- external or internal blood loos with regenerative anemia and low serum protein levels
- spontaneous bleeding is not typically observed until numbers are < 50*10^9/L
What would be your diagnostic plan to investigate a cat with thrombocytopenia
Routine hematology
- to look for other cytopenias, RBC morphology changes
Diagnostic imaging
- thoracic radiographs and abdominal ultrasonography to look for underlying disease
Test for infectious diseases
- FIV, FeLV, FIP
Bone marrow analysis
- if other cytopenias are evident or if there is no evidence of platelet regeneration as indicated by the presence of large “shift” platelets
How would you manage a cat suffering thrombocytopenia
Animals with platelet counts < 50*10^9/L should be considered at risk of imminent, potentially life threatening hemorrhage
Strict rest should be instituted
Avoid procedures that may induce hemorrhage (e.g., IM injections, cystocentesis
IV fluid support or blood transfusions should be administered as required
- blood transfusion will not increase the number of platelets for a patient and is given for the treatment of blood loss only
Treatment of the underlying disease
- e.g., immunosuppressant drugs if immune-mediated thrombocytopenia is suspected
What is the prevalence of thrombocytopathies in cats
Problems with platelet function are rare in cats
- hereditary disorders such as Chediak-Higashi syndrome and collagen deficiency have been shown to cause platelet dysfunction
What is the clinical profile of cats with acquired platelet dysfunction
Animals with acquired platelet dysfunction generally do not have episodes of spontaneous hemorrhage, although bleeding can be significant after invasive procedure (e.g., biopsies or surgery)
What would be your differentials for acquired platelet dysfunction in cats
Possible causes of acquired platelet dysfunction in cats include:
- liver disease
- renal failure
- neoplasia
- immune-mediated thrombocytopenia
- drugs (e.g., aspirin)
How would you investigate disorders of primary hemostasis
Manual platelet count
Buccal mucosal bleeding time (N< 4 min)
What are the principal features of immune mediated thrombocytopenia in cats
IMTP is less prevalent compared too dogs but it is being recognised more commonly
Cats may present with symptoms such as epistaxis and tend to be young
It is often associated with a sever thrombocytopenia (< 10*10^9/L)
Primary IMTP carries a good prognosis and many cats will respond to prednisolone alone
