Disorders of Haemostasis Flashcards
1
Q
Primary haemostasis
A
- results in platelet formation
- doesn’t involve coag pathways
2
Q
Quantitative and qualitative primary haemostasis
A
- qualitative; functional defect can be inherited or acquired
- quantitative; thrombocytopenia or thrombocytosis
3
Q
Acquired primary haemostasis
A
- drugs
- alcohol
- uremia
- myeloproliferative disorders
4
Q
What does the immediate arrest of haemorrhage depend on?
A
- formation of fibrin clot
- vasoconstriction
- adhesion
- aggregation
- activation of coag system
- leading to platelet plug
5
Q
Healthy endothelium
A
- expresses ecto-ADPase (CD39)
- produces prostacyclin (PGI2) and nitric oxide (NO)
- block platelet adhesion to and activation by healthy endothelium
- Also has active anticoagulant mechanisms
6
Q
Normal platelet count
A
- 150 - 350 x 10^9/L
7
Q
Thrombocytopenia platelet count
A
- <150 x 10^9/L
- mild: 50-150
- moderate: 20-50
- severe: <20
8
Q
Bleeding and platelet count
A
- Bleeding seldom occurs >50x10^9/L.
- Minor >10x10^9/L.
- Spontaneous <10x10^9/L.
- Clinical bleeding doesn’t always correlate with plt count due to other factors e.g. endothelium integrity and platelet functionality.
9
Q
Diagnosis of thrombocytopenia
A
- Full blood count.
- Blood fill: Number, size, plt colour
- Plt clumping - citrate sample
- Large plts - congenital thrombocytopenias or increased plt turnover
- Small plts – Wiskott-Aldrich
- RC fragments - thrombotic microangiopathy.
- Hypogranular neutrophils - myelodysplasia
10
Q
Aetiology of thrombocytopenia
A
- Exclude congenital thrombocytopenia’s - previous normal count
- Exposure to drugs e.g. Alcohol or quinine
- Viral infections e.g. HIV or CMV
- Post op; dilutional - will resolve, cardiac surgery - may persist
- autoimmune; ITP, Anti-phospholipid syndrome and post transfusion purpura
11
Q
Immune thrombocytopenia (ITP)
A
- Incidence 2.5/100k, >60yrs 4.5/100k
- Petechial rash or oral bleeding
- Platelets >50 - no treatment necessary
- usually acute, self limiting in children
- may be prolonged in adults
12
Q
Adult ITP
A
- <30 or bleeding - prednisone given
- <20 – hospitalised. Anti-D, IgG, Rituximab, cyclophosphamide splenectomy
13
Q
Thrombotic microangiopathies
A
- Include TTP, HUS, HELLP (Haemolytic anaemia with Elevated Liver enzymes and Low Platelet count) and HIT.
- Ischaemic injury to one or more organ or tissue.
- RC fragments, reticulocytosis, thrombocytopenia and raised LDH
14
Q
Treatment of thrombotic microangiopathies
A
- TTP - plasma exchange (ADAMTS13)
- HUS - withdrawal of drugs
- HELLP - delivery of foetus and placenta
- HIT - cessation of heparin and administration of antithrombotic agents
15
Q
Bernard Soulier GP Ib-IX-V
A
- platelet function defect
- Thrombocytopenia
- large platelets
- impaired binding of VWF (Von Willebrand factor)
- Poor platelet adhesion and aggregation
16
Q
Glanzmann thrombasthenia. GP IIb/IIIa
A
- platelet function defect
- Fails to bind fibrinogen.
- Platelet count is normal but no aggregation w/ agonists e.g. ADP, epinephrine and collagen
17
Q
Platelet transfusions
A
- Contraindicated in TTP and HIT
- Limited indications
- Transmit infections
- Sensitise recipient to platelet antigens – HLA matched platelets necessary.
18
Q
How would you diagnose a platelet functional defect?
A
- perform platelet aggregation tests
19
Q
Secondary haemostasis
A
- end of coagulation cascade is fibrin clot
- involve coag pathways; extrinsic, intrinsic, common
20
Q
Extrinsic pathway
A
- Main pathway for initiation of coagulation
- Exposure of tissue factor (TF) binds to FVII activating FX.
- Prothrombinase complex (FX, FV, calcium and plt phospholipid activates prothrombin to thrombin (a small amt)) which then activates FXI leading to intrinsic pathway
21
Q
Intrinsic pathway
A
- amplifies the coag cascade
- FIXa, FVIII, calcium and phospholipid (tenase complex) amplify FX activation generating large amts of thrombin.
22
Q
Thrombin
A
- part of intrinsic pathway
- cleaves fibrinogen to form soluble fibrin monomers which polymerise to form soluble fibrin polymer.
- then activates FXIII which with calcium cross links and stabilises the fibrin polymer forming cross linked (insoluble) fibrin.
23
Q
Positive feedback
A
- Thrombin activates FXI on the platelet surface which can activate FIX to enhance FXa generation
- High levels of thrombin can cleave PAR4 - plt shape change - Stabilisation of platelet plug
- High levels of thrombin generated at propagation phase bind to fibrin and are protected from inhibition by antithrombin.
24
Q
Localisation
A
- Thrombin released from the plt plug is swept downstream- antithrombin - half life of thrombin <1 minute.
- FXa is rapidly inhibited by TFPI.
25
Thrombin on healthy endothelial cells
- negative feedback loop
- binds to thrombomodulin causing conformational change - no longer cleave fibrinogen
- rapidly inhibited by protein C inhibitor; rapidly dissociates
- activated protein C and S inactivate FVa and FVIIIa, confines thrombin generation to site of injury
26
Fibrinolysis
- When injury is healed, the dissolution of the fibrin clot begins - Plasminogen is central enzyme.
- Activators are tissue plasminogen activator (t-PA) and urokinase (u-PA).
- Plasmin cleaves the fibrin network and releases FDP (D and E) and fibrinogen - fragment X and Y, can impair plt aggregation and fibrin polymerisation.
- Plasmin also inactivates FVa and FVIIIa
- u-PA precursor is mediated by FXIIa, kallikrein and by plasmin.
27
Fibrinolysis defects
- Hyperfibrinolysis – disposes to bleeding and thrombosis. Plasmin inhibitor and Plasminogen inhibitor 1 prevent this.
- Hypofibrinolysis – deficiencies of t-PA or u-PA, plasminogen, contact factors. Associated with thromboembolic disease
28
Factor I
- defects: afibrinogenaemia
hypofibrinogenaemia
dysfibrinogenaemia
- bleeding: spontaneous; spontaneous abortions/severe post-op, Asymptomatic/bleeding/ thrombosis
- treatment: Fibrinogen concentrate/FFP/Cryoprecipitate, Keep levels >1.0, Half-life 5 days, Treat every 3 days
29
Factor II
- defects: hypoprothrominaemia, dysprothrombinaemia
- bleeding: mild to severe bleeding , mucosal membrane bleeds
- treatment: Prothrombin complex concentrate (PCC)/ FFP
30
Factor V
- defects: autosomal recessive trait
- bleeding: mild bleeding in childhood, mucosal membranes/CNS
- FFP/Platelet Transfusions
31
Factor VII
- defects: rare autosomal disorder, heterozygotes – asymptomatic, acquired
- Moderate bleeding - mucous membrane, epistaxis and menorrhagia.
- Severe bleeding (homozygous) – bleeding into CNS (early onset) leads to high morbidity and mortality
- treatment: FVII concentrates, Novoseven, Half-life 5hrs
32
Factor VIII (Haemophilia A)
- 1 in 10,000 affected.
- X-linked.
- Most common mutation (up to 50%) in severe Haem A is a major inversion in Intron 22.
- Severe <1% - recurrent spontaneous bleeding.
- Moderate 1-5% -may be spontaneous bleeding, bleeding after trauma and surgery.
- Mild 5-50% - bleeding after trauma or surgery but no spontaneous bleeding.
33
Presentation of Haemophilia A
- Severe - 6-9months (earlier if intramuscular injection received).
- Mild /moderate usually present later dependant on levels.
- Common sites - joints, muscles, brain.
- Repeated hemarthroses leads to joint destruction. Compartment syndrome leading to necrosis and muscle shortening.
34
Treatment of Haemophilia A
- Treat until bleeding stops
- FVIII Concentrates - Beriate.
- Recombinant Prophylaxis – Recombinate, Refacto. Thrice weekly.
- Complication is the development of inhibitors (10-15%).
- New extended half-life factor concentrates - Elocta, Novo8
- Hemlibra; a novel antibody that mimics FVIII - subcutaneous injection licensed for Severe Haem A Monitored by a modified Factor VIII assay
35
Combined FV and FVIII
- Rare autosomal recessive bleeding disorder found around the Mediterranean sea.
- Moderate bleeding tendency.
- FV and FVIII levels - 5-30%.
- Normally due to a mutation in transport protein .
- Treatment: FVIII concentrate, FFP/ Octaplas
36
Factor IX (Haemophilia B)
- 1 in 50-100,000.
- Similar clinical picture to Haem A. Recurrent spontaneous joint bleeds occur.
- Bleeding in carriers more common.
- Treatment: Berifix, once daily. Refixia - pegulated FIX, different assay needed.
- Inhibitors are less common.
- Gene Therapy
37
Factor X
- One of the rarest autosomal recessive.
- Similar clinical picture to FVII.
- Due to the longer half-life 36hrs treatment can be given as Prothrombin complex concentrate or FFP daily.
- For major surgery FX is kept >30%. 10-40 % haemostatic
38
Factor XI (Haemophilia C)
- Ashkenazi Jews up to 13% population affected.
- Heterozygous have a partial deficiency, homozygous or compound heterozygous have severe deficiency.
- 3 mutations majority type II or III
- Type II – stop codon in exon 5. homozygous state results in levels ~1%.
- Type III Phe283 is replaced with Leu (missense mutation) results in levels ~10%.
- Type II/III heterozygotes result in levels ~3%
39
Factor XI deficiency
- can lead to excessive haemorrhage after surgery or trauma but doesn't cause bleeds into joints or muscles.
- Bleeding can be immediate or delayed
- lower limit normal range 60-70%. There is poor correlation between factor level and bleeding tendency.
- Heterozygotes level is 25-70 %
40
FXI treatments and complications
- Treatment: FFP or FXI concentrate (half life 52hrs).
| - Complications: thrombosis and inhibitors (type 2).
41
Factor XIII
- Rare autosomal recessive.
- Homozygotes present with life long bleeding from the umbilical cord.
- Spontaneous intracranial bleeds common. Spontaneous abortions in early pregnancy. Delayed wound healing.
- Rate assays used for determination of factor levels.
Levels >2% will allow normal haemostasis.
- Treatment: prophylactic FXIII concentrate monthly or at trauma.
42
Acquired deficiencies of FII, FV, FVII, IX and X
- Factor II - Autoantibody due to lupus- type anticoagulant.
- Factor V - transient after surgery, transfusion or aminoglycoside antibiotics.
- Factor VII - Very rare.
- Factor IX - very rare associated with post partum and SLE.
- Factor X - Amyloidosis
43
FVIII acquired deficiencies
- Development of inhibitors due to treatment or autoantibodies found in adults, postpartum women, immunological disorders and older patients >50 yrs. Evenly distributed between the sexes. - Presentation occurs with large haematomas
- Treatment: involves immunosuppressants (prednisone, cyclophosphamide) and Novoseven for bleeds.
44
Liver disease
- Prothrombin Time increases due to a decrease of extrinsic coag factors synthesised in the liver.
- As liver damage increases the APTT will also be affected.
- Also affects fibrinogen synthesis
45
Vitamin K deficiency
- affects production of Vit K dependent factors (FII, FVII, FIX, FX) causing an increase in the Prothrombin Time.
- Can be common in premature babies and patients with malabsorption conditions
46
Advantages of automation
- Reduces human error
- CTS reduces health and safety risks
- Large volume of work
- Reduction in assay time
47
Prothrombin time (PT)
- measure efficiency of EXTRINSIC pathway – FVII, FV, FX, FII or FI.
- Due to presence of excess TF, coag activation is independent from FVIII and FIX and less influenced by AT3/heparin.
- Add thromboplastin and calcium to citrated plasma. The time to clot formation is recorded.
- Normal range 13-20secs
48
Commonest causes of disorder for PT
- warfarin therapy
| - liver disease
49
Activated Partial Thromboplastin Time (APTT)
- assesses intrinsic pathway and common terminal sequence
- phospholipid added to initiate coag as well as surface
- normal range 27-40secs
- deficiency of FXII, FXI, FVIII, FX, FV, FII or FI
- commonest causes of disorder: Haem B, Haem A
50
Thrombin time (TT)
- assesses common terminal sequence
- sensitive to fibrinogen (I) or thrombin inhibition (IIa)
- commonest causes of disorder: disseminated intravascular coagulation (DIC) and heparin therapy
51
Fibrinogen
- based on addition of an excess of thrombin to platelet poor plasma
- fibrinogen concentration becomes rate-limiting factor and clotting time is a function of fibrinogen concentration
- increased concentration = shortened clotting time
- Not affected by heparin up to 1 U/ml, bilirubin to 21mg/dl, Hb to 375mg/dl.
- May be affected by degradation products
52
Further testing
- Once abnormal coag results have been found, second line tests can be done to investigate the cause.
- Thrombin Time (TT).
- Reptilase Time (RT)
- Protamine Time.
- Correction Tests.
- D-Dimer assay.
- Factor Assays.
- Dilute Russel Viper Venom Test.
- Lupus anticoagulant
53
Factor assays
- Patients plasma mixed with factor deficient plasma and the appropriate test repeated. - Time taken to clot can be read from graph to determine patient factor level
- Intrinsic factors: FVIII, FIX, FXI, FXII
- Extrinsic factors: FII, FV, FVII, FX
54
Anticoagulant therapy
- Agents inhibiting platelet function e.g aspirin.
- Warfarin.
- Heparin.
- Thrombin Inhibitors.
- FXa inhibitors.
- Thrombolytic agents e.g. streptokinase
- Natural Inhibitors of Coagulation
55
Warfarin
- Inhibits the vit K-dependent posttranslational modification of coag factors.
- Before release into circulation gamma carboxylation occurs converting ~10 glutamic acid residues in N-terminal regions to gamma-carboxyglutamates (Gla).
- catalysed by a carboxylase requiring O2, CO2 and reduced form of vit K (vit KH2). - Vit KH2 is oxidised to vitamin K epoxide which is recycled by vitamin K epoxide reductase and vitamin K reductase.
- Warfarin inhibits both, limiting the degree of carboxylation
56
International Normalised Ratio (INR)
- Monitored using the PT test.
- used for monitoring dose.
- INR is calculated according to; INR = PR^ISI
- PR is Prothrombin Ratio (clotting time of patient/ mean normal clotting time)
- ISI is the International Sensitivity Index which is a lot specific correction factor established against the WHO reference preparation.
57
Heparin
- complexes with Anti-Thrombin III to inhibit thrombin and increase clotting time.
- ATIII complexed to heparin is 1000-fold more efficient at binding thrombin due to a conformational change
- Other serine proteases are inactivated by the Heparin-ATIII complex – FXa
- Chromogenic Anti-Xa assays measure effect of low molecular weight heparins e.g. Tinzaparin, Fragmin, Danaparoid and Orgaran.
- Some ranges given as 0.3-0.6 U/ml.
58
Direct Oral Anticoagulants
- Thrombin inhibitor: Dabigatran (14-17hrs), PT^, APTT^, TT^
- Xa inhibitors: Rivaroxaban (7-11hrs), Apixaban (8-15hrs)
PT^, APTT^, TT not affected
