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6/9/2017 Clotting and Bleeding Disorders FRCEM SuccessDashboard Subscription expires in: 1 Days Extend
You have scored 32%
You answered 26 correct out of 81 questions.
Your answers are shown below:
Regarding the inheritance of haemophilia A, which of the following statements is CORRECT:
a) All daughters of a female carrier will become a carrier.
b) Daughters of a female carrier have a 50 % chance of developing haemophilia.
c) All sons of a female carrier will develop haemophilia.
d) All sons of a male haemophiliac will develop haemophilia.
e) All sons of a male haemophiliac will be unaffected.
Something wrong?
Haemophilia A is the most common of the hereditary clotting factor de ciencies. The inheritance is X-linked recessive;
sons of a female carrier have a 50 % chance of developing the disease, daughters have a 50 % chance of being a carrier,
all sons of a male haemophiliac will be unaffected, all daughters will be a carrier. This assumes the other parent is a non-
carrier.
The defect is an absence or low level of plasma factor VIII (factor VIII activity < 1% is considered severe). Infants may
develop profuse post-circumcision haemorrhage or joint and soft tissue bleeds and excessive bruising when they start
to become active.
Recurrent painful haemarthroses and muscle haematomas dominate the clinical course of severely affected patients
and if inadequately treated lead to progressive joint deformity and disability. Prolonged bleeding occurs after dental
extractions or post-trauma. Spontaneous haematuria and gastrointestinal haemorrhage may occur.
The clinical severity of the disease correlates inversely with the level of factor VIII. The APTT is elevated but the PT is
unaffected, factor VIII levels are low.
http://frcemsuccess.com/rev/sc44/ 1/59
,6/9/2017 Clotting and Bleeding Disorders FRCEM Success
Haemophilia B (Christmas disease) is due to a factor IX de ciency. The inheritance and clinical features are identical to
that of haemophilia A but it is ve times less common.
Which of the following is primarily released from platelet alpha granules:
a) Thromboxane A2
b) Von Willebrand factor (VWF)
c) Serotonin
d) Hydrolytic enzymes
e) Ionised calcium
Something wrong?
The platelet surface coat has glycoproteins that are particularly important in platelet adhesion and aggregation.
Adhesion to collagen is facilitated by glycoprotein Ia. Glycoproteins Ib and IIb/IIIa are important in the attachment of
platelets to von Willebrand factor (VWF) and hence to vascular subendothelium and each other. The binding site for
IIb/IIIa is also the receptor for brinogen, which like VWF is important in platelet-platelet aggregation.
The platelet plasma membrane invaginates into the platelet interior to form a canalicular system which provides a
large reactive surface area to which the plasma coagulation proteins may be selectively absorbed and activated.
Plasma membrane phospholipids are particularly important in the conversion of factor X to Xa and prothrombin (factor
II) to thrombin (IIa).
Platelets contain three types of storage granule;
1. dense granules containing ADP, ATP, serotonin and calcium
2. alpha granules containing clotting factors, VWF, platelet-derived growth factor (PDGF) and other proteins
3. lysosomes containing hydrolytic enzymes
Primary activation by various agonists e.g. thrombin induces intracellular signalling, leading to the release of granule
contents which promotes further platelet aggregation and activation.
Platelets also produce thromboxane A2 which is important in secondary ampli cation of platelet aggregation to form a
stable platelet plug (and has powerful vasoconstrictive activity).
Prostacyclin (PGI2) synthesised by endothelial cells has the opposing effects by increasing the level of platelet cAMP
and inhibiting platelet granular release and is thus a potent inhibitor of platelet adhesion and aggregation on normal
endothelium (and a potent vasodilator). Other natural inhibitors of platelet function include nitric oxide, adenosine and
CD39 (which hydrolyses ATP/ADP).
Regarding disseminated intravascular coagulation (DIC), which of the following statements is
INCORRECT:
a) There is stimulation of both the coagulation cascade and of brinolysis.
http://frcemsuccess.com/rev/sc44/ 2/59
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a) There is stimulation of both the coagulation cascade and of brinolysis.
b) There is depletion of brinogen and all coagulation factors.
c) Thrombocytosis results in widespread platelet aggregation.
d) DIC most commonly presents with bleeding not thrombosis.
e) Thrombin levels are increased.
Something wrong?
Disseminated intravascular coagulation (DIC) is characterised by a widespread inappropriate intravascular deposition
of brin with consumption of coagulation factors and platelets. This may occur as a consequence of:
disorders that release procoagulant material into the circulation:
severe trauma
amniotic uid embolism
placental abruption
adenocarcinomas
liver disease
severe falciparum malaria
haemolytic transfusion reaction
anaphylaxis
snake bites
disorders that cause widespread endothelial damage or platelet aggregation:
endotoxaemia
Gram-negative and meningococcal septicaemia
certain viral infections
severe burns
hypothermia
This results in increased activity of thrombin in the circulation that overwhelms its normal rate of removal by natural
anticoagulants.
In addition to causing increased deposition of brin in the microcirculation and widespread platelet aggregation,
intravascular thrombin formation interferes with brin polymerisation. Intense brinolysis is stimulated by thrombi on
vascular walls and the release of brin degradation products again interferes with brin polymerisation. The combined
action of thrombin and plasmin causes depletion of brinogen and all coagulation factors, compounded by
thrombocytopaenia caused by platelet consumption.
DIC may be associated with a fulminant haemorrhagic or thrombotic syndrome with organ dysfunction or run a less
severe and more chronic course. The main clinical presentation is with bleeding (e.g. from venepuncture sites or
wounds, in the gastrointestinal tract, the oropharynx, into the lungs, the urogenital tract and from the vagina in
obstetric cases) but 5 – 10 % manifest thrombotic lesions (e.g. skin lesions, renal failure, gangrene of ngers or toes, or
cerebral ischaemia).
The platelet count is low, the brinogen concentration is low, PT and APTT are prolonged, there is a high D-dimer and
features of microangiopathic haemolytic anaemia may be present. Treatment is usually of the underlying cause.
Supportive treatment may be with blood transfusion and antiplatelet or anticoagulant therapy.
http://frcemsuccess.com/rev/sc44/ 3/59
, 6/9/2017 Clotting and Bleeding Disorders FRCEM Success
Supportive treatment may be with blood transfusion and antiplatelet or anticoagulant therapy.
Regarding clotting, which of the following statements is CORRECT:
a) Only the PT is prolonged in warfarin therapy.
b) Only the APTT is prolonged in heparin therapy.
c) The APTT and PT are not affected in von Willebrand disease.
d) Both PT and APTT are prolonged in haemophilia A.
e) PT is usually expressed as the INR.
Something wrong?
The activated partial thromboplastin time (APTT) measures the intrinsic pathway and the common pathway. It is
dependent on factors I, II, V, VIII, IX, X, XI and XII. The normal time is 30 – 40 seconds.
APTT is prolonged in haemophilia A and B, liver disease, DIC, massive blood transfusion, warfarin therapy, heparin
therapy and Von Willebrand disease.
The prothrombin time (PT) measures the extrinsic and common pathway. It is dependent on factors I, II, III, V, VII, X.
The normal time is 10 – 14 s. It may be expressed as the international normalised ratio (INR).
PT is prolonged in liver disease, DIC, massive transfusion, warfarin therapy (grossly), heparin (mildly).
Platelets are derived from which of the following cell types:
a) Macrophages
b) Promyelocytes
c) Megakaryocytes
d) Metamyelocytes
e) Monocytes
Something wrong?
The normal haemostatic response to vascular damage depends on a closely linked interaction between the blood
vessel wall, circulating platelets and blood coagulation factors.
Platelets are produced in the bone marrow by fragmentation of the cytoplasm of megakaryocytes, derived from the
common myeloid progenitor cell. The time interval from differentiation of the human stem cell to the production of
platelets averages 10 days.
Thrombopoietin is the major regulator of platelet formation and 95 % of this is produced by the liver. The normal
platelet count is 150 – 400 x 109/L and the normal platelet lifespan is 10 days. Old platelets are destroyed by
phagocytosis in the spleen and liver. Under normal circumstances, about one-third of the marrow output of platelets
http://frcemsuccess.com/rev/sc44/ 4/59
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