Platelet Disorders

What can increase platelet clumping in your sample collection?

Heparin

What are the two automated methods of evaluating platelet concentration?

impendance and optical

What is the impendance method?

based on size only

What is the optical method?

size and granularity

When should a slide estimate be used?

when automated PLT is falsely increased or full CBC is not feasible; usually less accurate than automated methods

What is mean platelet volume (MPV)?

provides the average volume (size) of platelets

What is the normal expectation for size of platelets?

should be uniform in most species

What animals are the exception and do not have uniformly sized platelets?

cats

What is determined with an increased MPV?

immature platelets which indicated increased thrombopoieisis, abnormal platelets, and platelet clumping

What is determined with a decreased MPV?

platelet microparticles from incomplete phagocytosis by macrophages

What is plateletcrit (PCT)?

measure of circulating platelet mass by direct measurement of platelet layer in buddy coat and calculated

What are macroplatelets?

large/giant forms due to increased thrombopoiesis (immaturity) in dogs

Why is macroplatelets common in cats?

inherited tubulin defects

What is anaplasma platys?

morula (clusters of elementary bodies) in platelets of dogs; NOT nuclear fragments

What is considered a non-pathogenic, self-resolving infection due to a reoccurrence cyclically of severe thrombocytopenia followed by dissipation?

anaplasma platys

What are the causes of thrombocytopenia? (SPUD)

sequestration/spurious

decreased production

increased utilization

increased destruction

What is the panic value of PLT for most species?

<25,000-50,000 - risk of spontaneous bleeding

What is spurious thrombocytopenia?

most commonly due to platelet clumping especially in cats and EDTA-induced in horses

What is sequestration thrombocytopenia?

may occur with splenomegaly mainly in horses with potential sequela of sedation

What is decreased production thrombocytopenia?

generalized marrow failure or magakaryocytic hypoplasia/aplasia (rare)

What is increased utilization thrombocytopenia?

due to systemic or localized coagulation activation

What is increased destruction thrombocytopenia?

immune thrombocytopenia in dogs causes cytotoxic T cell destruction; diagnosis of exclusion

What breed is known for congenital macrothrombocytopenia?

Cavalier King Charles Spaniel have fewer, larger platelets making platelet mass normal so PCT is best to measure

What is a thrombopathy?

abnormal platelet function, platelet concentration is within reference interval

What is a thrombopathy associated with dobermans?

von Willebrand’s disease

What is von Willebrand’s disease?

platelet number is adequate but they are unable to bind to exposed collagen resulting in failure of clot formation

What are the clinical signs of Von Willebrand’s Disease?

mucosal bleeding, increased bleeding at sites of tissue injury, NO petechiation

Why is petechiation not a clinical sign seen with Von Willebrand’s disease?

adequate platelet growth factors are available to promote healthy endothelial barrier

What is vWF (Von Willebrand’s disease) a carrier protein for?

FVIII (factor 8) prolongs its half-life circulation leading to prolonged PTT

What are the laboratory findings for congenital thrombopathies?

PLT is WRI, prolonged buccal mucosal bleeding time, decreased vWF concentration

What are acquired thrombopathies?

certain drugs can increase the risk of bleeding; cyclooxygenase inhibitors such as NSAIDs and aspirin

What is pseudothrombocytosis?

erroneous counting of cell fragments or particulate cellular debris; artifact

What are the causes of pseudothrombocytosis?

ghost erythrocytes and lipemia

What is the most common cause of thrombocytosis?

inflammatory diseases

What can cause a transient thrombocytosis?

splenic contraction