Hemostasis: Approach to a Patient

Question 1

What cell is described as small anuclear discoid or 2-3 microns and is derived from megakaryocytes?

Answer 1

Platelets

Question 2

How long does it take for a platelet to mature?

How long is the lifespan of a platelet?

Answer 2

• 4-5 days

- 9-10 days

Question 3

What percentage of platelets are found in circulation?

In the spleen?

Answer 3

80% in circulation

20% in spleen

Question 4

What are megathrombocytes?

Answer 4

Newly formed platelets that are large in size

Question 5

Platelets contain ____________ but do not contain ____________

Answer 5

Mitochondria

Nuclei

Question 6

What are the three kinds of functional granules found in a platelet?

Answer 6

Dense
Alpha
Lysosomal granules

Question 7

What do dense granules contain?

Answer 7

ATP
ADP
Serotonin
Calcium

Question 8

What do alpha-granules contain?

Answer 8

A number of proteins essential for platelet funciton including procoagulant proteins, plaelet-specific factors for platelet activation, and growth favtors

Question 9

What do lysosomal granules contain?

Answer 9

Acid hydrolases

Question 10

What is the function of surface-connected canalicular systems?

Answer 10

These extensive systems of internal membrane tunnels are tunnels through which the contents of the platelet granules are extruded during platelet aggregation and secretion

Question 11

What are the main functions of platelets?

Answer 11

Adhesion to the vascular subendothelium at sites of injury

Activation of intracellular signaling pathways leading to cytoskeletal changes and release of intracellular gransules

Aggregation to form the platelet plug

Support thrombin generation

Question 12

Intact endothelial cells can produce what two compounds that act as inhibitors of platelet activation?

Answer 12

Nitric oxide and prostacyclin

Question 13

What factor do platelets bind in order to adhere to injured endothelium?

Answer 13

von Willebrand’s Factor

Question 14

What protein is used to link vWF to platelets?

Answer 14

GP1b

Question 15

What is the role of GPIIb-IIIa in platelet and vWF adhesion?

Answer 15

The enzyme increases its affinity

Question 16

What happens after platelets adhere to the injured vessel wall?

Answer 16

They undergo a shape change through cytoskeletal activation, becoming more spherical with extended pseudpods and spread over the exposed subendothelium

Then they release the granules

Question 17

Platelets adhere to each other through which protein?

Answer 17

Fibrinogen is a cross-linker between GPIIb-IIIa

Question 18

What converts fibrinogen to fibrin to form a stabilized plaatelet plug?

Answer 18

Thrombin

Question 19

What two tests are commonly used to evaluate platelet function?

Answer 19

Platelet count as a part of a CBC

Bleeding time which will be prolonged if

Question 20

This type of QUALITATIVE platelet disorder is characterized by as a disorder in adhesion. It is the most common congenital bleeding disorder. It leads to a primary and secondary bleeding disorder. What is it?

Answer 20

Von Willebrands disease.

Question 21

What test can you use to test the activity of vWF?

Answer 21

Ristocetin cofactor activity test

Question 22

What drug can you use to treat type I vWD?

Answer 22

DDAVP because it enhances the release of vWF from endothelial stores

Question 23

What is Bernard-Soulier syndrome?

Answer 23

A rare autosomal recessive disorder where expression of GP1b on the platelet surface is reduced

Abnormal ristocetin test

Question 24

What is gray platelet syndrome?

Answer 24

Deficiency in dense granules or alpha-granules

Question 25

Afibrogenemia is a rare inherited defect that results in a decreased amount of what protein?

Answer 25

Fibinogen

Question 26

What rare autosomal recessive bleeding disorder is characterized by the absence of defective GPIIb-IIIa?

Answer 26

Glanzmann thrombasthenia

Question 27

What is the normal platelet range?

Answer 27

150,000-400,000

Question 28

At what platelet count could you expect patients to spontaneously hemorrhage?

Question 29

At what platelet count could you expect patients to spontaneously hemorrhage intracranially?

Answer 29

10-20,000

Question 30

What is the most common cause of thrombocytopenia due to increased destruction?

Answer 30

Immune thrombocytopenic purpura

Question 31

What are the two forms of ITP?

Answer 31

Acute and chronic

Question 32

What patient population do you usually see acute ITP?

Answer 32

Children and young adults after a viral infection | Onset is sudden and severe

Question 33

What patient population do you usually see chronic ITP?

Answer 33

In adult patients with other autoimmune disorders, lymphoma, or HIV. Or idiopathic Most patients require treatment

Question 34

What are three treatments for patients with chronic ITP?

Answer 34

1. Corticosteroids 2. IVIG 3. Splenectomy

Question 35

What is alloimmune thrombocytopenia?

Answer 35

Occurs when a patient develops antibodies to platelet antigens not present on the patient's own platelets

Question 36

What is the mechanism of drug induced immune thrombocytopenia?

Answer 36

Drug binds to the platelet surface glycoprotein and creates a neooepitope

Question 37

Name some nonimmune-mediated causes of thrombocytopenia.

Answer 37

DIC sepsis thrombotic thrombocytopenic purpura (TTP) hemolytic uremic syndrome (HUS)-more often in children presents like TTP but with a majority of renal failure. association with bacterial toxin *All of these disorders are due to increased platelet consumption

Question 38

Thrombotic thrombocytopenic purpura (TTP) is characterized by fever, renal insufficiency, microangiopathic hemolytic anemia, mental status changes, and thrombocytopenia. They have characteristic large vWF multimers. This deficiency is caused by a decrease in what protein?

Answer 38

ADAMTS13 which normally digests the vWF into smaller multimers

Question 39

Is thrombotic thrombocytopenic purpua more commonly congenital or acquired?

Answer 39

Acquired due to the development of autoantibodies to ADAMTS13

Question 40

What is the treatment for thrombotic thrombocytopenic purpura?

Answer 40

Pheresis of vWF and replacement of missing ADAMTS13

Question 41

Name some basic bleeding tests used to evaluate excessive bleeding.

Answer 41

``` Platelet count and blood smear Bleeding time and PFA-100 APTT PT/INR Thrombin clotting time Fibrinogen level ```