Haematology and Oncology Flashcards
What’s the pathophysiology underlying TTP?
ADAMST3 activity deficiency! Either acquired (95%) or genetic mutation (5%)
This protease normally breaks down ultra large polymers of vWF.
Failure to do so. = platelet clumping, micro-thrombi and red cell fragmentation.
What are the steps involved in primary haemostasis (platelet plug)?
1) Platelet adhesion to damaged vessel wall (GP1a-collagen) and GP1b-vWF)
2) Platelet activation via interaction with one another and with collagen and mediated by thrombin. Involves release of contents of alpha and dense granules.
3) Platelet aggregation (ADP released from dense granules binds to Platelet P2Y12 receptor activating the GPIIB/IIIa complex. The aggregation happens through the linking of platelet exposed GPIIB/IIIa complexes with fibrinogen and vWF
Describe the extrinsic pathway (initiation phase)
Extrinsic pathway involves TF on exposed tissue vessel wall after injury
TF binds FVII -> FVIIa
FVIIa binds FX -> FXa….
FXa interacts with cofactor FVa to activate prothrombin (FII) -> thrombin (FIIa)
Thrombin activates platelets, activates fibrinogen and also stimulates FV, FVIII and XIII
Describe the intrinsic pathway
Intrinsic pathway is activated by contact with -be charged surfaces (in Vivo by expose of subendothelial CT of damaged vessels).
Deficiencies of factors don’t usually cause bleeding
Process…
FXII interact with -ve charge surface -> FXIIa
FXIIa binds FXI -> FXIa
FXIa binds FIX -> FIXa
FIXa activates FX -> FXa
FXa enters common pathway
Describe the final common pathway of haemostasis
FXa activates FII (prothrombin) -> FIIa (thrombin)
This process involves cofactors FV, Calcium and happens on platelet surface.
FIIa (thrombin) hydrolyses FI (fibrinogen) -> FIa (fibrin)
Fibrin monomers aggregate
FIIa (Thrombin) activates FXIII -> FXIIIa
FXIIIa links (FXIa) fibrin polymers to form insoluble fibrin clot.
Describe Fibrinolysis
Fibrinolysis = process of breaking down fibrin and fibrinogen
Activators of fibrinolysis:
tPA - secreted by endothelial cells
Urokinase - released by macrophages
Factor XIIa ( intrinsic pathway)
Process:
tPA bind fibrin then activates plasmin from plasminogen.
Activated Plasmin then cleaves fibrin and fibrinogen to fibrin degredation products and D dimers.
NB. D dimers are specifically products of cross linked fibrin breakdown
Describe the processes involved in natural anticoagulation
1) Preventing platelet activation and aggregation
Endothelial cells secrete vasodilatory and anti platelet substances:
i) NO - inc cGMP - dec intracellular Ca -> vasodilation and inhibits platelet aggregation
ii) PGI2 - vasodilates. Prostacyclin also binds directly to platelet surface preventing their activation ( Gs GPCR)
2) Preventing fibrin clot formation
Tissue Factor inhibitor - expressed on the surface of the normal endothelium and inhibits extrinsic pathway
Antithrombin III - inhibits thrombin as well as intrinsic pathway factors -
Thromomodulin is a protein which modulates thrombin and this activates Protein C
(NB - thrombin also activates Protein C)
Protein C with the help of Protein S - inhibits cofactors V and VIII
3) Fibrinolysis
Process of plasmin breaking down fibrin and fibrinogen to FDP.
Plasminogen is activated to plasmin by 1) Urokinase, 2) tPA 3) Factor XIIa
PT test and causes of prolonged PT
PT (play tennis outside!)
- tests extrinsic pathway
- thromboplastin added to citrated blood
- time taken to clot measured
- normal 10-13 secs
- tests FI, II, VII, X
- INR = ratio of sample PT to international standard, warfarin therapy
Abnormal prolonged PT
- warfarin
- FII, FVII deficiency -> remember II/VII/IX and X need Vit K
- Vit K deficiency
- DIC
- Artefact - incorrect sampling or if Hct is high
APTT test and causes of abnormal result
Remember play table tennis inside!
- tests intrinsic pathway
- kaolin added to citrated blood
- tests factors XII, XI, IX, VIII and factors common to both pathways.
- Normally 30-35secs
Causes of prolonged APTT
- Heparin
- Haemophillia - A (factor VIII def)
- Haemophilia- B (factor IX def)
- Liver disease
- DIC
Mixing tests are performed in cases of prolonged APTT to determine if it is a true factor deficiency or there is an inhibitor present. (Mix sample with normal blood 50:50 - if APTT corrects it was a factor deficiency…if it remains prolonged do further tests for inhibitor…
Antiphospholipid syndrome causes prolonged APTT which doesn’t correct with mixing blood sample with 50:50 normal platelet free plasma
Adding heparinise, if heparin is present and causing prolonged APTT, the result will normalise when heparin activity is inhibited.
Describe the thrombin time and causes of abnormal result
- Thrombin is added to undiluted plasma
- common pathway assessment
- Tests time to conversion of fibrinogen FI -> fibrin FIa
Prolonged in:
- DIC
- heparin activity (inhibits thrombin by potentiating antithrombin )
- low fibrinogen levels
- direct thrombin inhibitor
Causes of an abnormal fibrinogen
High - acute phase protein
Low - sepsis and DIC
Describe classic features of TTP
FAT R/N
- Fever
- Anaemia
- Thrombocytopenia
-Renal problems ( more so HUS > TTP)
-Neuro problems ( TTP > HUS)
Principles of Mx of TTP
1) Replacement
- Plasma exchange
- FFP or cryo replacement ( has ADAMST13)
- 1.5 plasma volumes daily until plt > 150
2) Immune modulation
- Steroids - methylpred for 3 /7
- If neuro or cardiac involvement -> Rituximab ( monoclonal Ab which binds to CD20 on B cells to inhibit autoantibody production)
3) Can inhibit vWF with ? Caplacizumab
Why do coagulation mixing studies?
Mixing Studies help differentiate between factor deficiencies or factor inhibitors
If your sample of plasma is giving a high PT or aPTT - grab your suspicious plasma sample, and mix it with normal blood, 50:50. Obviously, if some sort of “factor inhibitor” is present, the normal blood will also be affected, and the resulting mixture will give abnormal aPTT and PT results. If there is a factor deficiency, the mixed sample will result in a normal PT or aPTT.
An abnormal mixing study result implies that in spite of the addition of normal plasma, the coagulopathy persists. This suggests that a factor inhibitor is present.
Go onto check antiphospholipid anticoagulant and heparin assay
What will prolong your PT and your APTT?
- DIC
- Massive transfusion
- Massive warfarin overdose
- Primary fibrinolysis - e.g in trauma
- Post thrombolysis
- Snake bite - which can be pro or anti-coagulant
- Direct thrombin inhibitor toxicity - thrombin time should be prolonged in this case but reptilase time normal
Severe liver failure
List some of the common thrombophilia’s
Thrombophilia = predisposition to clotting!
- Antithrombin III deficiency ( inherited or acquired)
- Protein C deficiency ( normally inhibits FV + FVIII)
- Protein S deficiency (assists Protein C)
- Lupus anticoagulant
- Prothrombin gene mutation
- Factor V Leiden mutation
What are the causes of Antithrombin III deficiency
ATIII is a protein, it inhibits thrombin activity. ATIII also inhibits intrinsic pathway CF.
Deficiency may be:
- Hereditary or;
- Acquired (reduced production, inc. consumption or protein loss)
- Reduced production -> Liver disease
- Increased consumption -> DIC, ECMO / CRRT circuits
- Protein loss -> nephrotic syndrome, major blood loss, plasmapheresis where replacement fluid is albumin
How do you manage Antithrombin III deficiency ?
- AT III concentrate
- FFP if concentrate not available
NB if using heparin for VTE prophylaxis - may not work at all or demonstrate resistance if ATIII deficiency
What does the Thrombin time measure?
- Thrombin time measures conversion of Fibrinogen ( FI) -> fibrin ( F1a)
- Prolonged Thrombin Clotting Time ( TCT) seen in low fibrinogen levels, heparin use or the generation of fibrin degradation products
What is the Ecarin Clotting time test?
- Ecarin is a snake protease
- it activates prothrombin (FII) bypassing the intrinsic and extrinsic systems
- therefore insensitive to the most part of the clotting system (eg effects of heparin / warfarin or on cases of factor depletion)
- it IS a useful test for direct thrombin inhibitors
Advantages of TEG over fixed ratio massive transfusion
*patient specific POCT - guided transfusion
*reduce unnecessary products
*Teg detects fibrinolysis and
hyperfibrinolysis
*faster than traditional clotting profile
*can be used to demonstrate medical vs surgical cause of coagulopathy - I.e can exclude medical causes of bleeding in trauma patient
Define Tumour Lysis Syndrome
TLS is an oncological emergency resulting from massive turnover and lysis of tumour cells causing release of potassium, phosphate and nucleic acids (urate is product of metabolism) into the circulation. Hypocalcaemia is also seen.
Results in:
*High K
*High PO4
*High Urate
*Low Ca
List the risk factors associated with the development of TLS
Patient related RF:
- Lymphomas. esp Burkitts
- Leukaemia’s
- High burden of disease
-some solid tumours - e.g. breast, testes
-CKD
-Nephrotoxics
-Dehydration
-Gout
Treatment related RF:
- aggressive chemo
-specific agents e.g….
- R-CHOP - e.g. rituximab, cyclophosphamide, vincristine, doxorubicin, prednisilone
Principles of prevention of tumour lysis
*Anticipate
*Hydrate - enhance renal clearance of solutes and reduce r/o precipitation of urate crystals
*Frequent Electrolyte monitoring - K, Ca, Urate, PO4, UEC
Specific Rx:
*Allopurinol = xanthine oxidase inhibitor to reduce urate formation
*Rasburicase = recombinant urate oxidase, enhances degradation of urate to allatonin which is more soluble and excreted renally
Management of Tumour Lysis Syndrome
*Hydration and diuresis - to maintain volume and enhance renal clearance of K/PO4/Urate
*Rasburicase = recombinant urate oxidase to enhance degradation of urate to allantonin which is more soluble and renally excreted
*Treat electrolyte abnormalities e.g hyperkalaemia and symptomatic hypocalcaemia
*Haemodialysis, for standard indications; severe electrolyte abnormalities, oliguria, fluid overload, acidosis.
Basics of TEG or ROTEM
*Viscoelastic tests are POC tests of whole blood clotting
*Blood is added to cuvette ( cup) with suspended pin at 37degrees
*TF / kaolin added
*Rotation motion occurs and the resistance developing to rotation measured and displayed graphically
*In TEG the cup spins ( T - cup)
*In ROTEM the pin spins
List some of the uses for TEG
*Trauma
*Post cardiac surgery
*Post liver transplant
*To guide massive transfusion
*DIC
*Peripartum period
TEG interpretation of values
R time
*Reaction time - time from latency to initial fibrin clot formation
*dependant on CF
K time:
*time from end of R to certain fibrin clot strength
*dependant on fibrinogen
alpha angle:
*rate of fibrin clot strength
*dependant on fibrinogen
Max amplitude:
*Peak clot strength
*80 % dependant on platelets, 20% on fibrinogen
LY30:
*percentage decrease from MA after 30 mins
*correlates to rate of fibrinolysis
TEG as a guide to Treatment (by R/K/alpha/MA/LY30)
Prolonged R time = deficient CF = give FFP
Prolonged K time = deficient fibrinogen = give cryo
Decreased alpha angle = deficient fibrinogen = give cryo
Decreased MA = decreased overall clot strength = give platelets or DDAVP
Decreased Lysis 30 time = enhanced fibrinolysis = need TXA
List advantages and disadvantages of TEG/ROTEM
Advantages:
POCT
Tests whole blood coagulation
Real time evaluation of clot formation
Can test fibrinolysis - which normal coags cant
Predictor of post operative hypercoagulation states
Quick than full coagulation test
May guide balanced transfusion
Reduces products in e.g. cardiac surgery
Sensitive to heparin effect
Disadvantages:
Requires user training
Machine recalibration is needed frequently
Doesn’t measure effects of hypothermia
Describe the normal ROTEM tests
INTEM: Measures intrinsic pathway (APTT), phospholipid added
EXTEM: Measures extrinsic pathway (PT), TF added
FIBTEM: Measures fibrinogen function by using platelet inhibitor to block the platelet contribution to clotting
APTEM: uses aprotinin to inhibit fibrinolytic proteins. It is otherwise identical to EXTEM. A shortened CT (R time) and a higher MCF in an APTEM test ( c/w) EXTEM) suggest that hyperfibrinolysis is taking place.
Additional:
HEPTEM: heparinase added to sample - removes effect of heparin. A significantly shortened HEPTEM time c/o INTEM would suggest presence of heparin e.g. in CPB
ECATEM: Ecarin is a prothrombin ( FII) activator. In the presence of direct thrombin inhibitors the ECATEM will be prolonged
Classification of Heparin Induced Thrombocytopenia
HIT 1:
*benign
*non immune
*mild aggregation resulting from PF4/heparin complexes
*mild thrombocytopenia ~ plt count 100
*self limiting on cessation of heparin
*up to ~ 10% of patients on heparin
*no associated thrombosis
HITT 2 ( thrombosis and thrombocytopenia)
*life threatening
*IgG mediated antibodies to PF4/Heparin complex
*subsequent thromboycytopenia ( macrophage mediated)
*thrombosis and consumptive thrombocytopenia from activation and aggregation
*incidence higher with UFH > LMWH
*requires anticoagulation
Pathophysiology of life threatening HITTs
IgG mediated response to PF4/Heparin complexes
“Anti PF4 antibodies”
IgG coated platelets taken up by macrophages = thrombocytopenia
Abnormal platelet activation and aggregation = arterial and venous thrombosis
Anaphylactoid reactions can occur to heparin due to Ab presence
Risk factors for HIT and pre-test probability
R/F = cancer, trauma and surgery (increase PF4 release)
4T score:
- Thrombocytopenia severity
- Timing - day 5-10 most common, unless prior exposure to heparin
- Thrombosis presence
- Thrombocytopenia possibly due to other causes?
Indications for IVC filter placement
NB Weak evidence base:
-recurrent PE on full anticoagulation
- patients with absolute CI to anticoagulation
( e.g. SAH with unsecure aneurysm or HITTS (II) unable to use alternative agent)
-Life threatening proximal DVT (e.g ileofemoral) despite anticoagulation
-high risk trauma patients: ( TBI / Spinal / Pelvic #)
List advantages /disadvantages of IVC filters
Advantages:
- May decrease r/o of fatal PE in patients with HIGH risk DVT e.g. proximal iliofemoral even on anticoagulation
= Can be used to reduce r/o PE in patients with absolute contraindication to anticoagulation - Newer devices are removable
Disadvantages:
- Weak evidence base for their use
- Insertion complications - failure / vessel injury/ perforation / air embolus
- Delayed complications - infection / IVC clot with thrombosis -> venous stasis, IVC can occlude ( 20% patients at 5 years), device # and displacement risks
- IVC filters don’t prevent new DVT formation
Causes of thrombocytopenia
Platelet < 150
1) Pseudothrombocytopenia
- clumping
2) Dilution:
- Massive transfusion (also causes platelet consumption)
-Fluid resuscitation
3) Reduced Production ( BM suppression or infiltration)
-Drugs e.g. linezolid / valproate
-Viral infection
-Liver disease (reduced thrombopoeitin)
-B12 / folate deficiency
-Haematological malignancy
4) Increased destruction:
-Drugs - heparin / antiplatelets
-Sepsis
-DIC
- Immune - ITP
-TTP
-HUS / HELLP
-Haemolysis ( MAHA)
-Intravascular circuit loss - CBP / ECMO / Dialysis / IABP
- Sequestration:
-splenomegaly - e.g. malaria and other causes - increased aggregation
- sepsis
-MODS
-Massive PE
Thrombocytopenia work up
General approach to likely cause involves history, examination and investigation:
Basic bloods:
1) blood film - clumping / spherocytes / signs of infiltration
2) LFTS - liver disease causing dec thrombopoietin?
3) B12 / Folate
4) Haemolytic screen
5) Coags - ?DIC
Infection screen:
1) Viral - EBV / CMV/ Malaria if splenomegaly / HIV / Hepatitis
2) Septic screen
Disorder specific:
1) Vasculitis screen
2) ADAMST13 activity - for TTP
3) ELISA Test for PF4 antibody - HITTS
4. BM aspirate: malignancy / aplastic anaemia
What is the ECHIS coagulation time
ECHIS is a snake venom added to blood sample which activates prothrombin without requiring vitamin K.
If PT prolonged but ECHIS time normal = Vit K deficiency or warfarin use
If ECHIS time and PT prolonged then liver dysfunction present (ie factor deficient)
What is a HITT screen
HITT screen performed if preprobability (4T score) is high (4 or more) for HITTS.
Test is an immunoassay for anti PF4 antibodies.
Sensitive but not specific
Don’t perform if pre test probability is low
NB gold standard test for HITTS is a functional assay if the pre test probability was high and the screen is equivocal.
Mechanism of DDAVP action on platelet function in bleeding
- V2 vascular endothelial release of Vwf and FVIII enhanced
- Increases the density of platelet surface glycoprotein receptors
- Enhances the ability to form procoagulant platelets and increases platelet-dependent thrombin generation by enhancing Na+/Ca2+ mobilisation.
- Thus, increases platelet aggregation
It is not a blood product, and can be used in bleeding Jehovah’s witnesses
What is von willebrand disease? What are the types, investigations and treatment options?
*most common inherited bleeding disorder ( 1-2% prevalence)
*Autosomal dominant
*results in abnormal platelet adhesion and prolonged bleeding time
Types:
1) mild form, reduced vWF levels ( ~ 90% cases)
2) dysfunctional vWF -> DDAVP is CI
3) absent vWF -> most severe form
Ix:
Plt count will be normal
Prolonged bleeding time
APTT might be slightly prolonged ( due to decreased FVIII)
vWF level and FVIII level correlate with disease severity
Mx:
-DDAVP if patient is DDAVP responder ( as prophylaxis 0.3mcg/kg)
-Consider Replacement therapy with FVIII or vWF
-Consider cryo as source of vWF is acute bleeding
-avoid antiplatelets
List the common causes of macrocytosis
MCV>100
*alcoholism
*B12/folate def
*myelodysplastic syndromes
*chronic liver diseases
*hypothyroid
*chemo / valproate / trimethoprim / metformin
What are RBC rouleaux and list some causes
Rouleaux are stacks of RBC which abnormally aggregate together
Causes are anything which increases your ESR -> Infection / dehydration/malignancy e.g. multiple myeloma
