Bleeding disorders Flashcards
What are the components of the blood haemolytic system? (3)
Plasma coagulation factors
Platelets
Blood vessel wall
What are the main 4 steps of the blood haemostatic system?
- Trigger
- Primary haemostasis
- Thrombin generation
- Thrombin consolidates clot formation
Explain the steps of the blood haemolytic system (7)
STEP 1: TRIGGER
- Collagen and tissue factor exposed
- Von Willebrand Factor (vWF) binds to collagen
STEP2: Primary haemostasis
- Platelets adhere to vWF-collagen
- Platelets activate and aggregate.
STEP 3: Thrombin generation
5. TF initiates rapid thrombin generation on activated platelets
Step 4: Thrombin consolidates clot formation
- Thrombin converts fibrinogen to fibrin and completes platelet activation.
- Stable fibrin-platelet clot is formed.
END PRODUCT: Stable cross-linked clot
What causes thrombin production?
Tissue factors exposed to coagulation factors
What is primary haemostasis?
When platelets adhere to vWF-collagen and platelets activate and aggregate.
What can go wrong with the coagulation pathway? (2)
- Abnormal primary haemostasis
> Reduced platelet number or function
> Reduced Von Willebrand factor - Abnormal coagulation pathway?
> Reduced clotting factors (e.g. factor VIII)
Is abnormal skin bleeding a primary haemostasis or coagulation disorder?
Primary haemostasis
Is deep tissues bleeding a primary haemostasis or a coagulation disorder?
Coagulation disorder
What are the patterns of bleeding for primary haemostasis disorders? (5)
- Petechiae/bruising
- Epistaxis
- Gum bleeding
- Menorrhagia
- GI/CNS bleeds
What are the patterns of bleeding for coagulation factor disorders? (3)
- Bleeds into joints
- Soft tissue bleeds
- CNS/GI bleeds
How do you identify people with abnormal haemostasis? (2)
- Clinical Evaluation
> Bleeding history is very sensitive to underlying bleeding disorders.- after previous dental procedures or surgery
- after minor trauma
> Family history of bleeding
> General medical history
> Drug history
- Laboratory evaluation
- Full blood count
> platelet count (but not platelet function) - Clotting screen
> ‘PT’ and ‘aPTT’ indicate whether coagulation factors are functioning.
How does the full blood count check for bleeding disorders?
Looks at platelet count (not function)
How does a clotting screen check for bleeding disorders?
What is PT?
What is aPTT?
What would be shown if there is abnormal function of coagulation factors?
PT = prothrombin time aPTT = activated partial thromboplastin time
these indicate if coagulation factors are functioning
abnormal function usually gives increased PT and/or increased aPTT
What is INR and what does it show?
INR = international normalised ratio
ratio of patient PT to ‘normal’ PT
Why do you have to be careful with laboratory evaluation? (3)
> not all bleeding disorders cause abnormal FBC, PT or aPTT.
> abnormal FBC, PT or aPTT doesn’t necessarily mean bleeding
> further specialist tests are always required to make specific diagnosis
e.g. Factors assays. Factor VIII down so Factor VIII deficiency (Haemophilia A)
What are the classifications of bleeding disorders (3)
Give examples for each
- INHERITED DISEASES
- Haemophilia A
- Von Willebrand disease - ACQUIRED DISEASES
- Thrombocytopenia (e.g. immune thrombocytopenia, chemotherapy)
- Kidney disease
- Liver disease - ANTI-THROMBOTIC DRUGS
What is Von Willebrand disease?
It is reduced circulating levels of vWF resulting in abnormal bleeding.
most common genetic bleeding disorder.
Maybe no abnormalities in PT/aPTT/PLT
What are the symptoms of Von Willebrand disease?
Abnormal primary haemostasis
What are the symptoms of abnormal primary haemostasis? (4)
- Epistaxis
- Gum bleeding
- Heavy menstrual bleeding
- Skin bleeding - (don’t confuse with non-accidental injury)
What are the treatments to prevent bleeding in mild Von Willebrand disease? (2)
explain how they work and their route of entry
- Tranexamic acid
- tablets or mouthwash
- reduced clot break-down (antifibrinolytic)
> tranexamic acid stabilises fibrin clot formed and prevents premature breakdown by fibrinolytic enzymes such as plasmin. - Desmopressin (DDAVP)
- subcutaneous or intranasal
- releases endogenous vWF
What is immune thrombocytopenia?
Immune-mediated destruction and reduced platelet production due to autoantibody production.
What causes immune thrombocytopenia?
Idiopathic or after viral infection, exposure to some drugs.
How can you diagnose immune thrombocytopenia in a lab?
reduced platelet count (PLT) (<10x10^9/L)
What are the symptoms of immune thrombocytopenia?
abnormal primary haemostasis
similar to vWD + skin purpura if PLT<10
how do you treat immune thrombocytopenia? (2)
long term disease control
–> immunosuppression with steroids or other agents
treatment of bleeding: --> tranexamic acid --> local measures --> intravenous immunoglobin platelet transfusion only in life threatening bleeding
How does liver disease cause bleeding disorders?
The liver synthesises most clotting proteins and regulates platelet production.
A decrease in clotting factor and fibrinogen levels because of reduced synthesis and vitamin K malabsorption.
This causes a decreased PLT number because of reduced thrombopoietin synthesis
There is a decreased PLT function bec of metabolic disturbances
There is an increased clot breakdown (fibrinolysis
What are the clinical features of liver disease?
skin, soft tissue and GI tract bleeding.
subconjunctival haemorrhage and jaundice
oesophageal varices form portal hypertension
How can you detect liver disease in the laboratory?
increase PT
increased aPTT
decreased fibrinogen
decreased PLT count
Does chronic liver disease show stable abnormal clotting test results often without bleeding?
yes
How do you treat bleeding in liver disease? (2)
NO TREATMENT NEEDED IF NOT BLEEDING AND STABLE
IF BLEEDING:
Tranexamic acid
Vitamin K
Consider fresh frozen plasma - contains all of the different coagulation factors and fibrinogen
What are antithrombotic drugs?
drugs that affect haemostasis
they’re widely prescribed.
all can cause bleeding
What are the 2 categories of anti-thrombotic drugs?
- Anti-platelet drugs
2. Anti-coagulant drugs
What do anti-platelet agents do?
what are they used to prevent/treat?
they inhibit platelet function.
prevent or treat arterial thrombosis (acute coronary syndromes, stroke, peripheral arterial thrombosis)
What do anti-coagulant drugs do?
What do they prevent/treat?
They inhibit the coagulation pathway.
Prevent or treat venous thrombosis (deep vein thrombosis, pulmonary embolism, stroke in arterial fibrillation or in pts with mechanical heart valve).
name some examples of antiplatelet drugs.
Aspirin
Clopidogrel
Drugs with ‘unintentional’ anti-platelet effects e.g. NSAIDs
These drugs cause no abnormalities in standard lab tests as they affect platelet function.
Name some examples of anti-coagulant drugs. (3)
- Warfarin
- Novel Oral Anti-Coagulants/Direct oral anti-coagulants (NOACs/DOACs) (rivaroxaban, apixaban, edoxaban, dabigatran)
- Low molecular weight heparin
others (except warfarin) don’t cause major abnormalities in test results except in overdoes.
How does warfarin work?
Warfarin acts by diminishing availability of vitamin K in liver and therefore reduces synthesis of several coagulation factors.
It causes prolonged PT and is monitored using INR test.
INR range for most warfarin indications is 2-3.
How do you manage bleeding risk for dental procedures?
What are the general principles?
different procedures counter different risks of bleeding.
different anti-thrombotic drug regimes confer different risks of bleeding.
bleeding is undesirable..but in some cases stopping antithrombotic drugs may increase the risk of breakthrough thrombosis.
FOR MOST PROCEDURES THE LIKELIHOOD OF BLEEDING IS LOW AND STOPPING ANTI-THROMBOTICS IS UNCOMMON
it is reasonable to delay the plan for dental treatment if pt is on a short term course of antithrombotics.
Explain how you would manage a pt with warfarin before surgery?
Check INR no more the 24 hours before procedure.
If INR is below 4 treat without interrupting medication.
actively consider suturing and packing
If INR is above 4, delay treatment.
