Session 5 ILO'S Haemostasis Flashcards
Describe and begin to interpret the common tests in a coagulation screen.
3 main coagulation tests : (To check for clotting defects)
- Test done on platelet poor plasma
- APTT (activated partial thromboplastin time)
- Reflects the intrinsic pathway
- If Prolonged (takes a longer time for blood to clot than normal = most commonly due to a deficiency in factors: 8, 9, 11, 12
- Deficiency in 8 (haemophilia A)
- Deficiency in 9 (haemophilia B) - PT (prothrombin time)
- Reflects the extrinsic pathway
- Prolonged PT is most commonly due to factor 7 deficiency
If the APTT alone or the PT alone is prolonged, we can deduce what factors are deficient.
However if deficiency in factor 5, 10, thrombin or fibrinogen, both PT and APTT will be prolonged as both are involved in the common pathway.
- TCT (thrombin clotting time)
- Reflects the final step of the common pathway = conversion of fibrinogen to fibrin (via action of thrombin)
- can be prolonged in inherited or acquired deficiencies of fibrinogen, or abnormal fibrinogen
- TCT is impaired in the presence of heparin and in the presence of raised levels of fibrinogen degradation products
Recognise and discuss some common inherited bleeding disorders
e.g. Haemophilia A & B
Haemophilia A: (3) - X-linked recessive (so usually affects males only) - Congenital lack of factor VIII (8) - Prolonged APTT and a normal PT - Treatment: (2) Recombinant factor 8 DDAVP (Desmopressin)
Haemophilia B = ‘Christmas’ disease:
- X-linked recessive
- Congenital lack of factor 9
- Prolonged APTT and a normal PT
- Treated with infusions of recombinant factor 9
Haemophilia signs/symptoms:
- Muscle haematomas
- Reccurent Haemarthroses (bleeding into joints)
- Joint pain and deformity
- Life threatening prolonged Post operative and post traumatic bleeding
- Intracerebral hemmorage
Recognise and discuss some common inherited bleeding disorders
e.g. Von-Willebrand disease.
(please cross reference with semester 1 modules with the genetic aspects)
Von-Willebrand disease: (7)
- Autosomal dominant (affects males and females)
- Several genetic defects cause this condition
- vWF usually carries factor 8 and mediates platelet adhesion to the endothelium
- vWF deficient - type 1 and 3 (most common) or defective type 2
- Abnormal platelet adhesion to vessel wall
- Reduced Factor 8 amount/activity
- Diagnosed by a normal platelet count with prolonged bleeding time (defective platelet function)
- Symptoms:
Unnoticed until additional stress
Spontaneous bleeding from mucous membranes (nosebleeds)
Excessive bleeding from wounds
Mennorhagia (heavy menstrual bleeding)
Recognise and discuss some common inherited bleeding disorders
e.g. thrombophilia
(please cross reference with semester 1 modules with the genetic aspects)
Thrombophilia:
- Congenital or acquired defects of haemostasis which can increase a patient’s risk of thrombosis
• Congenital causes include:
– deficiency in natural anticoagulants (protein C, protein S and antithrombin)
– abnormal factor V 5 (factor V Leiden) – resistance to APC (Activated protein C)
• Acquired causes include antiphospholipid syndrome (due to antiphospholipid antibodies)
Recognise and discuss the treatment of disseminated intravascular coagulation.
Treatment:
- Treat underlying cause first!!
- Give platelets in the meantime to help improve coagulation
- If let untreated, can get haemorrhages and bleeding from end organs and mucosae
Recognise and discuss the pathophysiology of disseminated intravascular coagulation.
Disseminated intravascular coagulation:
Pathophysiology:
- Type of microangiopathic haemolytic anaemia due to the pathological activation of coagulation
- Numerous microthrombi are formed in the circulation which leads to consumption of clotting factors and platelets and a haemolytic anaemia
- Due to failure of haemostasis, the end result is hemmorage
Recognise and discuss the causes of disseminated intravascular coagulation.
- Always a another underlying cause
Causes/triggers: (6)
- Malignancy
- Massive tissue injury e.g. burns
- Massive haemorrhage and transfusion
- ABO transfusion reaction
- Infections (G -ve sepsis)
- Obstetric causes (placental abruption, pre-eclampsia, amniotic fluid embolism)
Recognise and discuss the symptoms of disseminated intravascular coagulation.
Symptoms: (5)
Symptoms are due to tissue hypoxia and infarction or haemorrhage:
- Respiratory compromise
- Convulsions and neurological symptoms
- Renal & hepatic failure
- Shock and cardiac failure
- Gangrene of the skin
Which clotting tests are affected in DIC?
- On investigation, blood test would show: (4)
- Raised PT/INR
- Raised APTT
- Raised D dimers
- Low fibrinogen and platelets
Describe the role of the vessel wall
Defect in blood vessel wall initiates the process:
- Vasoconstriction
- Production of vWF (platelet adhesion, carrier of Factor 8)
- Exposure of collagen and tissue factor initiates activation of clotting factors
Describe the role of the platelets and the platelet plug
The exposure of tissue factor and collagen results in platelet:
- Adhesion:
⇒ Platelets adhere to collagen via VWF ( a receptor)
- Activation:
⇒ Platelets secrete ADP, thromboxane, and other substances to become activated and activate other platelets
⇒ Platelets release factors that activate the clotting cascade
⇒ Provide some coagulation factors by secretion from internal stores
- Aggregation:
⇒ Platelets crosslink to form a platelet plug, which provides some stability but it’s friable
Describe the role of thrombin inhibitors
- Deactivate free thrombin and the thrombin bound to fibrin
- Thus prevent the formation of blood clots, reducing the risk for stroke or other medical conditions
Describe the coagulation system
Define and describe the principles of haemostasis i.e the role of the vessel wall, platelets and the platelet plug, the coagulation system, the fibrinolytic system and plasmin, the production of thrombin and fibrin and the role of thrombin inhibitors
Describe the the fibrinolytic system and plasmin
