GP- platelet disorders, hemostasis, and coagulation

disorders of hemostasis are common in what animals?

dogs

what is primary hemostasis?

the first step of hemostasis, where the vessels constrict and the platelet plug is formed

the endothelial damage causes the exposure of collagen, attracting platelets. the von willebrand factor allows the platelets to adhere to collagen.

what is secondary hemostasis?

the second step of hemostasis, where the platelet plug is turned into a clot.

both the intrinstic and extrinsic pathways work towards the activation of factor X, which combines with proaccelerin to be able to convert prothrombin to thrombin, which converts fibrinogen to fibrin

the products of fibrinolysis are...

FDP and D dimers

activators and inhibitors of coagulation and fibrinolysis are normally in dynamic balance, but a failure of this equilibrium can result in....

abnormal bleeding OR risk of intravascular coagulation (thrombosis)

what is antithrombin III?

a natural anticoagulant produced by hepatocytes to prevent excessive clot formation

what roles do protein C and protein S have with coagulation?

they inhibit certain coagulation factors

they are dependent on vitamin K, so an animal with vitamin K deficiency will cause them to not work,

what are the main regulators of fibrinolysis?

PA inhibitor (impairs tPA)

antiplasmins (impair plasmin)

thrombocytopenia and thrombocytosis are bleeding disorders that affect ______ hemostasis. (primary/secondary)

primary

what may cause an individual to have thrombocytopenia?

increased use:

DIC

hemangiosarcoma

congenital

increased destruction

immune mediated

ehrlichiosis

vasculitis

low production

BM disease

what is thrombocytopathy?

a normal number of platelets, but they do not work

what are the reasons an animal might have thrombocytopathy?

hereditary

von willebrand disease

acquired

drugs

secondary to another disease (cushings, ehrlochiosis, renal disease, liver disease, etc)

do clotting factor deficiencies impact primary or secondary hemostasis?

secondary

what might cause the low production of platelets?

bone marrow disease

what can cause the increased destruction of platelets?

immune-mediated problem

ehrlichiosis

vasculitis

what can cause the increased use of platelets, leading to thrombocytopenia?

DIC

hemangiosarcoma

what are reasons an animal may not make enough clotting factors?

vitamin K deficiency (malnutrition, rodenticide)

congenital disease

liver failure

why might an animal abnormally use more clotting factors, leading to their deficiency?

DIC

what are the clinical signs of an animal with thrombocytopenia or thrombocytopathy?

petechiae

ecchymosis

mucous membrane and skin bleeding

hematuria

epistaxis

immediate bleeding after venipuncture

what are the clinical signs of an animal with a coagulation problem (clotting factor deficiencies)?

muscle and joint bleeding

bleeding into body cavities

hematomas

delayed bleeding after venipuncture

if an animal comes in with lots of petechiae, ecchymosis, and epistaxis, they probably have a problem with what part of hemostasis?

primary hemostasis

thrombocytopenia or thrombocytopathy

if an animal comes in with hematomas, muscle and joint bleeding, and hemothorax, they probably have a problem with what part of hemostasis?

secondary hemostasis

clotting factor deficiency

how can we diagnose a problem with primary hemostasis (thrombocytopenia/thrombocytopathy)?

-platelet count (with a machine)

-looking at platelet morphology (with a blood smear)

-bone marrow examination

-platelet function tests, like mucosal bleeding time

why is it important to perform a platelet count before surgery?

because if the animal has thrombocytopenia, surgery might cause a lot of unwanted bleeding, so we try to avoid it

why is the machine less reliable than a blood smear when doing a platelet count?

because if there are aggregations of platelets, it doesn't count these, so the platelet count will be very low

what numbers of platelets indicate thrombocytopenia?

<100-150 x10^3/L (with machine)

<3 per field (with blood smear)

what is mucosal bleeding time? what does it measure?

it is the time taken to stop bleeding after an incision made with a lancet on the upper lip, vaginal mucosa, or toenail cuticle

it tells us how well the platelets are working

the incision should stop bleeding after:

dogs- <4-5 min

cats- <2.5 min

horses- <10-14 min

if we perform a mucosal bleeding time test on a dog and it takes 6 minutes to stop bleeding, what is our conclusion?

he has a platelet problem: thrombocytopenia or thrombocytopathy. dogs should take 4-5 min to stop bleeding

if we perform a mucosal bleeding time test on a cat and it takes 2 minutes to stop bleeding, what is our conclusion?

his platelets are working normally

if we perform a mucosal bleeding time test on a horse and it takes 20 minutes to stop bleeding, what is our conclusion?

he has a platelet problem: thrombocytopenia or thrombocytopathy. horses should take 10-14 min to stop bleeding

how can we diagnose a secondary hemostasis disease?

with laboratory tests with machines:

prothrombin time

activated partial thromboplastin time

fibrinogen

thrombin time

which coagulation pathway does an activated partial thromboplastin time test evaluate?

intrinsic and common

what is von willebrand disease?

a congenital defect, causing the inability of platelets to adhere to a vascular injury. it is common in dobermans

is von willebrand disease a thrombocytopenia, thrombocytopathy, or clotting factor defect?

thrombocytopathy- there are normal numbers of platelets, but they cannot adhere properly

what is hemophilia A?

a sex linked factor VIII deficit (only males are asymptomatic)

what problems with coagulation does a vitamin K deficit cause?

a deficit in factors II, VII, IX, and X

problems with secondary hemostasis

why might an animal have a vitamin K deficiency?

ingestion of rodenticides- they have warfarin and brom adiolone, which inhibit vitamin K, causes GI issues, and damaged blood vessels, so the animal internally bleeds but cannot clot to stop the bleeding

liver disease or inflammatory bowel disease- cause problems in digesting vitamin K

how is rodenticide poisoning treated?

induce vomiting (if it was ingested recently)

activated charcoal (absorbs undigested poison in stomach)

oral vitamin K for 1 month

what is DIC?

disseminated intravascular coagulation

a problem with primary and secondary hemostasis, in which there is a widespread activation of the clotting cascade. this causes blood clots in the circulation, causing hypoxia and therefore organ damage. clotting factors and platelets are used up, so the animal internally bleeds more as well.

it is usually caused by an underlying condition like infections, sepsis, neoplasia, vascular disorders, toxins, pancreatitis

how can a hemangiosarcoma cause DIC?

it causes the release of factor X

this is common in german shepherds

how can pancreatitis cause DIC?

it causes tripsin activation, which causes endothelial damage, plasminogen activation, and activation of factors X and II

how is DIC treated?

heparin (anticoagulant)

blood transfusion

how do the laboratory tests of an animal with DIC appear?

low fibrinogen

thrombocytopenia

low antithrombin

schistocytes