Platelets: Qualitative & Quantitative Disorders

Question 1

State three functions of von Willebrand Factor (vWF)

Answer 1

• carrier protein for Factor VIII (VIII:C)
• participates in Platelet’s adhesion to subendothelial collagen
• Facilitates a normal aggregation response to ristocetin

Question 2

Discuss von Willebrand disease: Pathogenesis

Answer 2

Clinical disorder due to deficiency of von Willebrand factor

Question 3

Discuss von Willebrand disease: Bleeding time results

Answer 3

Increased

Question 4

Discuss von Willebrand disease: closure time results (PFA)

Answer 4

Increased

Question 5

Discuss von Willebrand disease: platelet adhesion result

Answer 5

Abnormal

Question 6

Discuss von Willebrand disease: platelet aggregation with ristocetin

Answer 6

Abnormal ristocetin induced aggregation

Question 7

Discuss von Willebrand disease: platelet count

Answer 7

can be normal or abnormal - not a hallmark

Question 8

Discuss von Willebrand disease: APTT result

Answer 8

Prolonged due to decrease VIII:C

Question 9

Discuss Bernard-Soulier syndrome: Pathogenesis

Answer 9

Missing GPIb/IX receptor complex: Platelets cannot adhere to subendothelium via vWF

Question 10

Discuss Bernard-Soulier syndrome: bleeding time result

Answer 10

Prolonged

Question 11

Discuss Bernard-Soulier syndrome: platelet aggregation with ADP & ristocetin

Answer 11

ADP: normal
Ristocetin: Abnormal

Question 12

Discuss Bernard-Soulier syndrome: platelet adhesion result

Answer 12

Abnormal

Question 13

Discuss Bernard-Soulier syndrome: platelet count

Answer 13

Decreased

Question 14

Discuss Bernard-Soulier syndrome: platelet morphology

Answer 14

Giant platelets

Question 15

Discuss Glanzmann’s thrombasthenia: Pathogenesis

Answer 15

Missing GPIIb/IIIa receptor complex: platelets cannot bind to fibrinogen and bridge/attach to one another—aggregate

Question 16

Discuss Glanzmann’s thrombasthenia: bleeding time result

Answer 16

Prolonged

Question 17

Discuss Glanzmann’s thrombasthenia: platelet adhesion result

Answer 17

Normal

Question 18

Discuss Glanzmann’s thrombasthenia: platelet aggregation with ADP and Ristocetin

Answer 18

ADP: abnormal
Ristocetin: normal

Question 19

Discuss Glanzmann’s thrombasthenia: platelet count

Answer 19

Normal

Question 20

Discuss Glanzmann’s thrombasthenia: platelet morphology

Answer 20

Normal

Question 21

List five acquired qualitative platelet disorders

Answer 21

• drug therapy (most common cause)
• Renal disease-uremia
• Dysproteinemias
• liver disease
• platelet antibodies

Question 22

List four general causes for thrombocytopenia.

Answer 22

• decreased platelet production
• ineffective thrombopoiesis
• abnormal distribution of platelets
• increased destruction of platelets

Question 23

Destruction occurs by processes other than the immune system (consumption, mechanical destruction).

Answer 23

Non-immune mediated platelet destruction

Question 24

Platelets become sensitized with antibody and RES, especially the spleen, destroys them

Answer 24

immune mediated platelet destruction

Question 25

List three causes of non-immune mediated platelet destruction for thrombocytopenia

Answer 25

• Thrombotic thrombocytopenic purpura (TTP)
• Hemolytic uremic syndrome (HUS)
• Disseminated intravascular coagulation (DIC)

Question 26

List three causes of immune mediated platelet destruction for thrombocytopenia

Answer 26

• Idiopthic thrombocytopenic purpura (ITP)
• drug-induced -> Heparin-induced thrombocytopenia (HIT)
• Neonatal alloimmune thrombocytopenia