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Haematology > Platelet abnormalities > Flashcards

Platelet abnormalities Flashcards

1
Q

Where are platelets produced?

A

Bone marrow cytoplasm

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2
Q

What are platelets?

A

Anucleate fragments of megakaryocytes

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3
Q

What is the lifespan of platelets?

A

7-10 days

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4
Q

Why is platelet lifespan shorter in bleeding?

A

Because they are being consumed

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5
Q

What happens to old platelets?

A

They are phagocytosed by splenic macrophages

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6
Q

What is the normal platelet count?

A

150-400 x10^9 /L

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7
Q

Give 3 important platelet receptors

A
  1. Thromboxane A2 (TXA2)
  2. P2Y12
  3. Glycoprotein IIb/IIIa
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8
Q

What does the thromboxane A2 (TXA2) receptor do?

A

Induces platelet aggregation and vasoconstriction

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9
Q

What is P2Y12 activated by?

A

ADP

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10
Q

What does the P2Y12 receptor do?

A

Amplifies activation of platelets and helps activate glycoprotein IIb/IIIa

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11
Q

What does the glycoprotein IIb/IIIa receptor do?

A

Acts as a receptor for fibrinogen and von Willebrand factor (vWF) and aids platelet adherence and aggregation

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12
Q

What test would you do to investigate platelet number?

A

Full blood count

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13
Q

What test would you do to investigate platelet appearance?

A

Blood film

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14
Q

What test would you do to investigate platelet function?

A
  • Platelet function analyser (PFA) i.e. response ti aggregating agents e.g. ADP, collagen
  • Bleeding time (unreliable)
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15
Q

What test would you do to investigate platelet surface proteins?

A

Flow cytometry

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16
Q

Give 4 clinical features of platelet dysfunction

A
  1. Mucosal bleeding 2. Easy bruising
  2. Petechiae, purpura
  3. Traumatic haematomas
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17
Q

Give some congenital conditions which reduce platelet function

A
  1. Storage pool disorders
  2. Glanzmann’s thrombasthenia
  3. Bernard Soulier syndrome
  4. von Willebrand disease
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18
Q

What is Glanzmann’s thrombasthenia?

A

Reduction/deficiency of fibrinogen receptor glycoprotein IIb/IIIa

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19
Q

What is Bernard Soulier syndrome?

A

Reduction/deficiency of von Willebrand receptor glycoprotein Ib

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20
Q

Give 2 conditions which will cause acquired platelet fuction problems

A
  1. Medication e.g. aspirin

2. Uraemia

21
Q

How does clopidogrel work?

A

It impairs P2Y12 receptor on platelets

22
Q

How does tirofiban work?

A

Interferes with glycoprotein IIb/IIIa receptor

23
Q

How does aspirin work?

A

It is a COX-1 inhibitor which inhibits arachidonic acid synthesis

24
Q

What is thrombocytopenia?

A

Deficiency of platelets in the blood

25
Q

What is congenital thrombocytopenia?

A

Absent/reduced/malfunctioning megakaryocytes in bone marrow

26
Q

Give some conditions which cause infiltration of the bone marrow

A
  • Leukaemia
  • Metastatic malignancy (breast and prostate)
  • Lymphoma
  • Myeloma
  • Myelofibrosis
27
Q

Name some conditions which can cause reduced platelet production by bone marrow

A
  • Low B12/folate
  • Reduced thrombopoietin (TPO) e.g. in liver disease
  • Medication e.g. methotrexate and chemotherapy
  • Toxins e.g. alcohol
  • Infections e.g. viral (HIV) or TB
  • Aplastic anaemia (autoimmune)
28
Q

Name a condition which can cause dysfunctional platelet production in bone marrow

A

Myelodysplasia

29
Q

Name an autoimmune condition which increases platelet destruction

A

Immune thrombocytopenia purpura (ITP) - primary or secondary

30
Q

Give some conditions which cause the increased consumption of platelets

A
  • Disseminated intravascular coagulopathy (DIC)
  • Thrombotic thrombocytopenic purpura (TTP)
  • Haemolytic uraemic syndrome (HUS)
  • Haemolysis, elevated liver enzymes and low platelets (HELLP) – often in pregnancy
  • Major haemorrhage
31
Q

What is immune thrombocytopenia?

A

IgG antibodies form against the platelet and megakaryocyte surface glycoproteins

32
Q

When might primary immune thrombocytopenia occur?

A

Sometimes after a viral infection/immunisation

33
Q

When might secondary immune thrombocytopenia occur?

A

In association with malignancies e.g. CLL or infections e.g. HIV, hepatitis C

34
Q

How might you treat immune thrombocytopenia?

A
  • Immunosuppression e.g. steroids, IV immunoglobulin
  • Treat underlying cause
  • Platelets if bleeding
  • Tranexamic acid
35
Q

What does tranexamic acid do?

A

Inhibits fibrin breakdown and is good to stop mucosal bleeding but not urinary tract bleeding

36
Q

What is disseminated intravascular coagulation (DIC)?

A

Small blood clots develop throughout the bloodstream, blocking small bold vessels

37
Q

What does SIRS stand for?

A

Systemic inflammatory response syndrome

38
Q

What happens in DIC?

A

Cytokine release in response to SIRS leads to a massive activation of the coagulation cascade

39
Q

What is the clinical presentation of DIC?

A
  • The patient is often acutely ill in shock
  • Bleeding
  • Bruising
  • Confusion
  • Thrombotic events
40
Q

What might you investigate in suspected DIC?

A
  • Look for underlying cause

* FBC, prothrombin time (PT), d-dimer

41
Q

Name some conditions which may cause SIRS

A
  • Sepsis
  • Major trauma and tissue destruction
  • Malignancy
  • Pancreatitis
  • Obstetric emergency
42
Q

How might you treat DIC?

A
  • Treat underlying cause

* Support with platelets, clotting factors, fibrinogen and blood transfusion if bleeding

43
Q

What is thrombotic thrombocytopenic purpura?

A

Spontaneous platelet aggregation in the microvasculature due to reduction in the protease enzyme ADAMTS-13

44
Q

What does the protease enzyme ADAMTS-13 do?

A

It is normally responsible for degradation of vWF

45
Q

Give some causes of thrombotic thrombocytopenic purpura

A
  • Idiopathic
  • Autoimmune e.g. SLE
  • Cancer
  • Pregnancy
  • Drug associations e.g. quinine
46
Q

What is the clinical presentation of thrombotic thrombocytopenic purpura?

A
  • Florid purpura
  • Fever
  • Fluctuating cerebral dysfunction
  • Haemolytic anaemia with red cell fragmentation, often accompanied by AKI
47
Q

How would you diagnose thrombotic thrombocytopenic purpura?

A
  • Coagulation screen is normal

* Lactate dehydrogenase is raised as a result of haemolysis

48
Q

How would you treat thrombotic thrombocytopenic purpura?

A
  • Urgent plasma exchange
  • Immunosuppression e.g. IV methylprednisolone
  • IV rituximab
49
Q

What should you not give in thrombotic thrombocytopenic purpura and why?

A

Platelets because this increases thrombosis

Haematology (5 decks)

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