HIS28 Inherited And Acquired Bleeding Disorder I Flashcards
Haemostasis
Body mechanism to
—> prevent excessive blood loss
—> stop excessive clot formation (i.e. prevent thrombosis)
Must be activated at appropriate TIME and appropriate SITE
Components:
- Blood vessel
- Platelets
- Coagulation factors
- von Willebrand factor
Blood vessel
- Keep blood fluid in normal state
—> inhibit haemostasis unless activated - Initiate haemostasis when endothelium damaged
—> Vasoconstriction
—> Collagen underneath exposed
—> Tissue factor released
von Willebrand factor
Produced by endothelium, circulating in plasma
- Bridge between platelet and collagen (sub-endothelial matrix) in platelet adhesion (via GPIb/V/IX complex)
—> bind to exposed collagen first
—> guide platelets to adhere to collagen (like an angel) - Carry and protect Factor 8 in circulation
—> without vWF
—> Factor 8 t1/2 very short (rapid degradation in plasma)
Functions of Platelets
Primary haemostasis
Structure:
- Membrane: **GP with specific functions + **Phospholipids
- Cytoplasmic granules: Alpha granules + Dense granules —> ***ADP, TXA2, 5-HT
Function:
1. Form primary haemostatic plug to close vascular defect
- adhesion to injured vessel
—> aggregation of platelets to each other
—> release
—> fusion
—> provide surface for coagulation cascade
- Release 5-HT and TXA2 to stimulate vasoconstriction
—> reduce bleeding + concentrate platelets/clotting factors at injury site - Clot formed by platelet is less stable (temporary)
—> provide surface for coagulation cascade
—> generate a stable fibrin clot
Platelet adhesion
- Primary adhesion
- vWF adhere to collagen
—> platelet adhere to vWF via GPIb/V/IX complex
—> activated platelet
—> Ca influx + signalling
—> platelet degranulation (ADP, TXA2, 5-HT)
—> trigger platelet degranulation + aggregation - Platelet-platelet tethering
—> release more platelet granules (+ve feedback)
—> platelet attach to each other via GPIIb/IIIa - Aggregation
Blood coagulation factors
Features:
- Enzymes and co-factors (Proteins mainly produced by liver)
- Factor 7 (shortest t1/2) and 8
- Factor 1 (fibrinogen) and 2 (prothrombin) (longest t1/2)
- other coagulation factors
2. Cascade —> Platelet —> TF (from damaged site) —> TF-7a complex —> Factor 10a —> Thrombin —> Fibrin + Factor 13a (cross link fibrin monomer —> stable fibrin polymer) + +ve feedback —> stabilised, cross-linked fibrin clot
- ***Amplification
- ***Positive feedback
- ***Activate platelets
End result: form ***stable (vs primary) haemostatic plug within short time
Current concept of coagulation
Initiated by 7a-TF complex
—> activate Factor 10
—> generate some Thrombin
—> activate Factor 5, 8 (positive loop) + Factor 9 (reinforce formation of tenase + prothrombinase) + Factor 11 (further activate Factor 9)
Endogenous anticoagulants (x rmb)
- Activated Protein C (APC)
- inhibit Factor 5a, 8a - αTHR
—> Clot can only be formed at injury site + injury time
***Evaluation of bleeding disorders
- History
- Personal (age of onset, severity, progression)
—> Inherited vs Acquired (much more common)
- Family history
- Trauma history? nature of trauma triggering bleeding?
—> no trauma history (spontaneous bleeding): bleeding disorder
—> profuse bleeding / bruising with minor injury: bleeding disorder
- Drug history - Pattern of bleeding
- **Mucocutaneous / Continuous oozing —> **Platelet / Vessel / vWF defect
- **Deep-seated (joint, soft tissue) / Delayed (re-bleeding after initial cessation) —> **Coagulation factors, Severe vWF deficiency (~ Factor VIII deficiency: Haemophilia A)
- Drugs (e.g. Warfarin) - Past surgical history (e.g. tooth extraction)
- any excessive bleeding - Menstrual history
- Associated systemic illness (e.g. liver / renal disease, autoimmune disease)
- Other symptoms of cytopenia
- anaemic symptoms
- fever (suggesting neutropenia / leukopenia as well —> Pancytopenia)
—> suggest BM disorder
***Mucocutaneous bleeding vs Deep-seated bleeding
Mucocutaneous bleeding (***Platelet / Vessel / vWF defect):
1. Bruising
2. Petechiae
3. Retinal bleeding
4. Menorrhagia
5. Oral mucosa / Gum bleeding
6. GI bleeding
Deep-seated bleeding (***Coagulation factors, Severe vWF deficiency):
1. Muscle haematoma
2. Haemarthrosis
3. Intracranial bleeding
***Tests for bleeding disorders
- Platelet
- count
- morphology
- function (platelet function test)
—> by aggregometry that measures aggregation response of platelets to different agonists
- **Numerical disorder (Thrombocytopenia)»_space;> Platelet dysfunction (except drug-induced platelet dysfunction)
- **Thrombocytopenia:
—> ↓ Production from BM
—> ↑ Consumption (immune / non-immune)
—> Abnormal sequestration in spleen (hypersplenism)
—> Dilutional (e.g. massive blood transfusion) - Coagulation factors
- functional assay for Factor level
- ***Coagulation screening test (in-vitro)
—> Prothrombin time (PT) —> test Extrinsic + Common pathway
—> Activated partial thromboplastin time (APTT) —> test Intrinsic + Common pathway
—> Thrombin time (TT)
—> Fibrinogen level - von Willebrand factor
- function
- amount
Coagulation screening test
Test:
- Prothrombin time (PT)
- Activated partial thromboplastin time (APTT)
- Thrombin time (TT)
- Fibrinogen level
Procedure:
- Exact volume of blood collected into bottle containing sodium citrate —> binds (remove) Ca —> anticoagulated blood
—> centrifugation
—> all coagulation factor + vWF are in plasma
—> add back necessary components (e.g. PT / APTT / TT reagent with appropriate amount of Ca + Phospholipid) to initiate clotting
Warfarin
MOA:
Antagonise Vit K action
—> reduce Factor 2, 7, 9, 10 (Vit K dependent factors)
—> ∵ Factor 7 short t1/2
—> changes in Factor 7 level well reflect therapeutic effect of Warfarin
—> ∴ use PT
Why need to monitor:
1. Narrow therapeutic index
2. Variable individual response
Prothrombin Time (PT)
Test for Extrinsic + Common pathway:
Extrinsic:
- Factor 7 (only factor in extrinsic pathway)
Common:
- Factor 10
- Factor 5
- Prothrombin (Factor 2)
- Fibrinogen (Factor 1)
International Normalised Ratio (INR):
- PT will vary with type of thromboplastin (PT reagent) used
- Individual thromboplastin calibrated against international WHO reference thromboplastin —> assign an International sensitivity index (ISI) (WHO standard: 1)
- ISI of test thromboplastin = ISI of WHO standard x slope of graph
- calibration with 20 normal people, 60 patients on Warfarin
- ***Use for Warfarin titration only!!!
- NOT use to monitor new oral anticoagulants
- NOT use to monitor DIC
INR = [PT of patient sample / mean PT of 20 normal people]^ISI of test thromboplastin
Activated Partial Thromboplastin Time (APTT)
Test for Intrinsic + Common pathway:
Intrinsic:
- Factor 12 (contact factor —> initiate coagulation)
- Factor 11
- Factor 9
- Factor 8
- Prekallikrein, Kallikrein, HMWK (contact factor —> initiate coagulation; level cannot be measured directly)
Common:
- Factor 10
- Factor 5
- Prothrombin (Factor 2)
- Fibrinogen (Factor 1)
***Interpretation of PT, APTT
- Isolated prolong PT
—> Factor 7 deficiency (most likely) - Prolong PT associated with Prolong APTT
—> Factor(s) deficiency / inhibitor in Extrinsic + Intrinsic / Common pathway
—> e.g. Vit K deficiency, Vit K antagonist (Warfarin), Liver disease - Isolated prolong APTT
—> Factor 12, 11, 9, 8 deficiencies
—> Inhibitors (AutoAb) of Factor 8 / other factors (rare) / Lupus anticoagulant (Anti-phospholipid syndrome: AutoAb target phospholipid —> APTT depend most heavily on phospholipid availability)
—> Contact factor deficiency (Factor 12, Prekallikrein, Kallikrein, HMWK)
—> Unfractionated Heparin
Thrombin Time (TT)
Test for Fibrinogen —> Fibrin:
Prolonged TT:
- Hypofibrinogenaemia (quantity)
- Dysfibrinogenaemia (quality, abnormal structure)
- Thrombin inhibition
- Inhibitor of Fibrinogen —> Fibrin
e.g.
1. Liver disease e.g. Cirrhosis (↓ synthesis / abnormal fibrinogen)
2. DIC (consumption of clotting factors / contain inhibitors of fibrinogen —> fibrin)
3. Heparin therapy (thrombin inhibition)
Interpretation of Fibrinogen level
Detected by functional assay (i.e. quantitative + qualitative):
↓ Fibrinogen level:
1. Liver disease e.g. Cirrhosis (↓ synthesis / abnormal fibrinogen)
2. DIC (consumption of clotting factors)
3. Inherited defects e.g. Hypofibrinogenaemia, Afibrinogenaemia, Dysfibrinogenaemia
↑ Fibrinogen level:
1. ***Acute phase reaction (acute phase protein) e.g. acute inflammation, sepsis, acute infection
2. Female sex, pregnancy, oral contraception (hormonal changes)
***Summary of Haemostatic test
- PT (extrinsic + common pathway):
- Factor 7
- Factor 5, 10, prothrombin, fibrinogen - APTT (intrinsic + common pathway):
- Factor 8, 9, 11, 12
- Factor 5, 10, prothrombin, fibrinogen - TT:
- Quantitative / qualitative defect of fibrinogen (Factor 1)
- inhibitors of fibrin formation
- inhibitors of thrombin - Fibrinogen level (by functional assay):
- Quantitative / qualitative defect of fibrinogen
In-vivo vs In-vitro coagulation
There is NO intrinsic / extrinsic pathway in in-vivo coagulation!!!
Different from in-vitro coagulation:
- Factor XII, Kallikrein, Prekallikrein, HMWK —> only required in in-vitro coagulation!!!
- In-vivo has anticoagulants e.g. Activated Protein C
***Workup of patient with Prolong APTT
Prolong APTT (most common problem for coagulation tests)
- Isolated APTT
—> Factor 8, 9, 11, 12, Contact factor deficiencies/inhibitors (most common factor 8 inhibitor)
—> Presence of Lupus anticoagulant - Associated with prolong PT —> then do TT / Fibrinogen assay
—> Normal TT (i.e. NOT involve fibrinogen to fibrin)
1. Vit K deficiency / antagonists (Factor 2, 7, 9, 10)
2. Common pathway factor deficiency / inhibitors (Factor 2, 5, 10)
3. Multiple factor deficiencies involving multiple pathway
—> Prolonged TT (+/- ↓ Fibrinogen level) (i.e. Involve fibrinogen to fibrin)
1. ***Liver disease (∵ quantitative / qualitative defect of fibrinogen)
2. Unfractionated Heparin (mostly TT + APTT prolong only)
3. Direct thrombin inhibitors (TT ↑↑ + APTT + PT prolong)
4. Afibrinogenaemia / Dysfibrinogenaemia / Hypofibrinogenaemia (TT + APTT + PT prolong)
5. DIC (all coagulation factors consumed)
Autoimmune thrombocytopenia (AITP) - Diagnosis of exclusion (排除曬其他野先consider)
Platelet sensitisation with **AutoAb (usually IgG)
—> premature removal from circulation by **Reticuloendothelial system (autoimmune haemolysis)
—> target antigens for AutoAb: ***GPIIb-IIIa / GPIb-IX
May occur:
1. Without identifiable antecedent / associated illness (typically in young / middle-aged adults, female predominant)
2. Secondary to other autoimmune diseases
3. Acute post-viral event (esp. young children)
Investigations:
- **Low platelet
- Exclusion of platelet consumption by other causes (e.g. DIC)
- BM exam show **adequate / even ↑ megakaryocytes
(- AutoAb on platelets/serum
- characterisation of antigenic specificity of AutoAb)
Alloimmune thrombocytopenia (very rare)
- Neonatal Alloimmune thrombocytopenia
- Fetomaternal incompatibility for human platelet antigen (HPA)
—> sensitisation of mother
—> Maternal AlloAb cross placenta
—> Thrombocytopenia in foetus (c.f. Haemolytic disease of newborn) - Post-transfusion purpura
- severe thrombocytopenia 1 week after transfusion (contains HPA-1a positive platelets) in HPA-1a negative patients previously sensitised to HPA-1a (Alloimmunised)
—> contain Ab against HPA-1a
—> **immune complex formed between released **HPA-1a antigen and Ab
—> adsorbed onto patient’s HPA-1a negative platelets
—> destruction of platelets - Platelet refractoriness
- Repeated failure to obtain satisfactory platelet count increment after transfusion of platelets
- AlloAb against donor platelets (mainly HLA Ab / Platelet specific Ab (less common))
Inherited Platelet disorders
Functional disorders (功能上差):
1. Defects of **Adhesion —> Bernard-Soulier syndrome —> Defect of GP Ib-IX, Thrombocytopenia, Giant platelets
2. Defects of **Release reaction —> Deficiency of α-granules (Grey platelet syndrome) / δ-granules (Storage pool disease)
3. Defects of ***Aggregation —> Glanzmann’s thrombasthenia due to defect of GP IIb-IIIa
Numerical disorder / Hereditary thrombocytopenia (數字上少):
1. Bernard-Soulier syndrome
2. Wiskott-Aldrich syndrome
3. May-Hegglin anomaly (giant platelets with Dohle body-like inclusions in neutrophils)
Inherited Coagulation disorders
- Haemophilia A
- deficiency of Factor 8
- genetic defect in Factor 8 gene on long arm of X chromosome (Xq28)
- X-linked
- positive family history of bleeding tendency on maternal side
- 1/3 new cases from spontaneous mutation - Haemophilia B
- less common than Haemophilia A
- deficiency of Factor 9
- genetic defect in Factor 9 gene on long arm of X chromosome (Xq26)
- X-linked
BOTH Clinical feature: **Haemarthrosis, Soft tissue bleeding, **Isolated prolong APTT
Differentiation by
***Clotting factor assay
- Haemophilia A —> low Factor 8 activity
- Haemophilia B —> low Factor 9 activity
Problems with Haemophilia A and B:
1. Recurrent bleeding in major joints —> progressive joint deformity
2. Inhibitor (AlloAb) to infused factor concentrate —> replacement therapy less effective
3. High cost of treatment
4. Transfusion transmitted infection e.g. HIV, HBV, HCV
5. Detection of carrier female: Phenotypic diagnosis (not always accurate) vs Molecular diagnostics (Factor 8 gene is a big gene, technically demanding)
-
**Von Willebrand disease (VWD)
- defect in vWF (qualitative / quantitative)
—> **Defect in platelet adhesion + ***↓ Factor 8 level
- gene for vWF on short arm chromosome 12 (12p)
- Autosomal inheritance
Clinical feature: ***Mucocutaneous bleeding, Isolated prolong APTT (∵ ↓ Factor 8 level)
Further tests for VWD:
- vWF antigen assay
- Ristocetin cofactor (RiCof) assay
- Collagen-binding assay
- Factor 8 assay
- Ristocetin-induced platelet aggregation test
- Factor 8 binding assay
- Multimeric study
Diagnosis of mild VWD can be difficult:
- Significant bleeding history
- Positive family history
- Compatible lab results (only on repeated testing)
(- Molecular diagnosis by next generation sequencing)
- Other
- very rare
- mostly ***Autosomal recessive
- Factor 12 deficiency NOT associated with bleeding
- Factor 7 deficiency: Isolated prolong PT
- Factor 10 deficiency: Prolong PT + APTT
- Fibrinogen deficiency / Dysfibrinogenaemia: Prolong PT + APTT + TT
Acquired bleeding disorders
- Vit K deficiency (common)
- Vit K antagonism (very common)
- Haemorrhagic disease of new born (very uncommon)
- Liver disease (very common)
- Uraemia (very common)
- ***DIC (common and clinically important)
Acquired bleeding disorder in details
- Vit K deficiency (common)
- Obstructive jaundice (i.e. no bile), Malabsoprtion state, Killing of intestinal flora by oral broad-spectrum antibiotics
- Vit K: fat-soluble, cannot be synthesised by human, must be absorbed from food in upper small intestine in presence of bile, some flora also produce Vit K
- required in γ-carboxylation of glutamic acid residues (post-translational event in hepatocytes)at amino-terminal domain of Factor 2, 7, 9, 10 (Vit K dependent clotting factor) + Protein C, Protein S (Naturally occurring anticoagulants)
—> Gla domain
—> able to bind Ca to adhere to platelet (biologically active) - Coagulation screening: Prolong PT, APTT, Normal TT
- Vit K antagonism (very common)
- oral anticoagulants (coumarin, phenindione derivatives) for primary / secondary prevention of thromboembolic disorders (competitive Vit K epoxide reductase inhibitor)
—> creates functional Vit K deficiency state
—> Prolong PT, APTT, Normal TT - Haemorrhagic disease of new born (very uncommon)
- immature liver to produce bile, sterile gut, low Vit K content in breast milk
—> prone to develop Vit K deficiency (if only breast fed and not given Vit K supplement) - Liver disease (very common)
- ALL coagulation factors (except vWF) (also Antithrombin, Protein C, S, Plasminogen, α2-antiplasmin) synthesised in hepatocytes
- Reticuloendothelial cells lining sinusoids clear activated intermediates of coagulation and fibrinolysis from bloodstream
- Acute / Chronic liver disease
—> **↓ Hepatic synthetic function —> ↓ clotting factors, inhibitors
—> **Thrombocytopenia (∵ Portal hypertension —> increased splenic sequestration i.e. hypersplenism)
—> **Cholestasis —> ↓ Vit K absorption —> ↓ active Vit K dependent factor + inhibitors
—> **Acquired dysfibrinogenaemia
—> ***Failure to clear activated intermediates of coagulation and fibrinolysis from bloodstream
- Coagulation screening: Prolong PT + APTT + TT
Treatment:
- Parenteral Vit K replacement (improve bleeding tendency)
- Clotting factor replacement by Fresh Frozen Plasma (FFP)
- Uraemia (very common)
- defects in platelet function + platelet-vessel wall interaction
- aggravated by low Hct
- **Mucocutaneous bleeding
- Coagulation screening: **Normal
Treatment:
- ↑ Hct (via RBC transfusion / erythropoietin therapy)
- Peritoneal / Haemodialysis
- DDAVP (Desmopressin) administration / Cryoprecipitate transfusion
-
**DIC (common and clinically important)
- **Inappropriate + Excessive activation of haemostasis
- Microthrombotic lesions (rare)
- Chronic + Compensated (if trigger is weak and persistent, usually no bleeding)
- Acute + Uncompensated (trigger strong enough)
—> **Widespread thrombosis + **Generalised haemorrhage
—> Tissue ischaemia
—> Multi-organ dysfunction
Causes:
1. Infections: septicaemia, viral infections
2. Malignancies: APL, metastatic carcinoma
3. Obstetric conditions: septic abortion, amniotic fluid embolism, abruptio placentae (early detachment of placenta from uterus)
4. Massive tissue trauma: extensive trauma / burns
5. Extensive IV haemolysis: ABO incompatibility
Pathogenesis:
1. Entry of tissue thromboplastin into blood
2. Direct activation of coagulation
3. Severe vascular endothelial injury
4. Direct activation of platelets
—> ALL leads to **Thrombin generation
—> **Fibrin generation (Widespread IV coagulation) + Secondary fibrinolysis
—> **Consumption of clotting factors, natural anticoagulants, platelets (*結血, 溶血都無曬)
Lab results:
- Prolong PT + APTT + TT + ↓ Fibrinogen (∵ consumed)
- ↑ Fibrin degradation products (***D-dimer) from Secondary fibrinolysis
- ↓ Platelet (Thrombocytopenia)
(- APTT may be normal due to elevated Factor 8 (acute phase protein)
- Fibrinogen may be normal ∵ acute phase protein)
Treatment:
- Remove precipitating trigger
- Control bleeding
- Frequent monitoring of coagulation screening
- Transfusion of platelet, fresh frozen plasma (supportive for bleeding)
