Alterations in Hemostasis

Question 1

What does an increased mean platelet volume can indicate?

Answer 1

Consistent with increased release of large or giant platelets and usually indicates a platelet regenerative response

Question 2

Why is the thrombocrit a better indicator of the total platelet functional potential?

Answer 2

Because larger platelets have greater functional capacity

Question 3

What are the three basic mechanisms of thrombocytopenia?

Answer 3

Platelet sequestration, decreased platelet production, and decreased platelet lifespan due to consumption or destruction

Question 4

What is usually the cause for increased platelet sequestration?

Answer 4

Splenomegaly

Question 5

What are the causes of splenomegaly?

Answer 5

• Infiltrative diseases - lymphoma, leukemia, and multiple myeloma
• Infectious or other inflammatory diseases - IMHA
• Lymphoid hyperplasia
• Splenic extramedullary hematopoiesis
• When venous outflow is compromised

Question 6

What can cause decreased platelet production?

Answer 6

Various bone marrow disorders

• Myelopthisis - replacement of normal marrow - often due to marrow infiltration with neoplastic cells
• Familial myelofibrosis - pygmy goats
• Toxic damage to the marrow (bracken fern toxicosis or NSAID administration
• Immune-mediated destruction of megakaryocytic
• Infectious agents - EIA, acute bovine viral diarrhea infection

Question 7

What can decrease platelet lifespan?

Answer 7

Destruction of platelets or platelet consumption in widespread coagulation

Question 8

What are the causes of immune-mediated thrombocytopenia?

Answer 8

• Idiopathic

- Secondary to various etiologies, including viral and bacterial infections, drug administration, and hemic neoplasia

Question 9

When do we have excessive consumption of platelets?

Answer 9

• With DIC - diagnosis of DIC relies on finding evidence of both platelet and coagulation factor consumption
• Snake envenomation directly causes platelet destruction without evidence of DIC

Question 10

What are the clinical signs of thrombocytopenia?

Answer 10

• Petechial or ecchymotic hemorrhages on the oral, nasal, and or vaginal mucosa
• Epistaxis, melena, hyphema and/or hematuria

Question 11

What are the causes of thrombocytosis?

Answer 11

• Physiologic - increase in high altitude
• Relative - redistribution from spleen and other organs
• Absolute - myeloproliferative disease, infectious and inflammatory disorders, iron deficiency

Question 12

What does the template bleeding time assess?

Answer 12

Primary hemostasis - platelet number/function and von Willebrand factor function

Question 13

What is Glanzmann’s thrombasthenia?

Answer 13

• Disorder resulting in poor platelet aggregation and clot retraction
• One or more defects in quantity or quality of platelet surface glycoprotein IIb/IIIa
• Has been reported as an hereditary dz in horses

Question 14

Which drugs impair platelet function?

Answer 14

Aspirin, phenylbutazone, sulfonamides, estrogens, and phenotiazines

Question 15

What does the prothrombin time assess?

Answer 15

Extrinsic and common pathways

VII, V, X, II

Question 16

Causes of acquired coagulation factors defects

Answer 16

Liver disease, vitamin K antagonism (moldy sweet clover poisoning), and increased consumption via DIC

Question 17

Vitamin K is necessary for the production of which coagulation factors?

Answer 17

II, VII, IX and X

Question 18

Causes of vitamin K antagonism

Answer 18

Coumarin compounds acquired via moldy sweet clover hay or anticoagulant rodenticide ingestion
Therapeutic administration (warfarin in horses)

Question 19

What does the activated partial thromboplastin time measures?

Answer 19

Intrinsic and common pathways

XII, XI, IX, VII, X, II, prekallikrein

Question 20

Liver disease and vitamin K antagonism prolong PT or PTT?

Answer 20

BOTH

Question 21

What do increased fibrin degradation products and d-dimers indicate?

Answer 21

Increased fibrinolysis in response to excessive coagulation

Question 22

What is the physiologically most important inhibitor of coagulation?

Answer 22

Antithrombin or antithrombin 3 - primarily neutralizes activated factors IX, X, and II

Question 23

What causes plasma ATIII levels to be reduced?

Answer 23

Decreased liver production, excessive use, loss from the intravascular compartment, increased catabolism, heparin administration

Question 24

Major clinical sequela of ATIII deficiency?

Answer 24

Venous thrombosis

Question 25

What can lead to hypofibrinogemia?

Answer 25

Impaired hepatic synthesis, increased consumption with DIC, uncompensated loss during massive hemorrhage

Question 26

What does thromboelastography assess?

Answer 26

Global clot formation and lysis in whole blood.

Question 27

Advantage of TEG over PT, PTT, and platelets?

Answer 27

Detects hyper coagulable states and increased fibrinolysis.

Question 28

What is the second major anticoagulant mechanism?

Answer 28

Protein C pathway