Coagulopathies 1&2 Flashcards
1
Q
Define haemostasis
A
The interaction b/w BVs, PLTs and coagulation factors that normally maintains blood in a fluid state and allows for formation of PLT plugs and clots when vessels are injured
2
Q
4 components of haemostasis
A
- endothelium
- PLT
- coagulation factors
- fibrinolytic factors
3
Q
Result of abnormal haemostasis
A
haemorrhage or thrombosis
4
Q
Outline endothelial cells in haemostasis
A
- flattened cells that line BVs
- have pro- and anticoagulant properties
- normally are anticoagulant
- act as barrier to subendothelial collagen which is procaogulant
5
Q
Describe von Willebrand’s factor (vWF)
A
- produced by endothelium and PLTs
- stored in Weibel Palade bodies
- released early in haemostatic process
- responsible for PLT adhesion to collagen
6
Q
Describe PLTs
A
- small, discoid, anuclear cells found in circulation
- 3-5 micrometers, pale basophilic, small red granules
- derived from cytoplasm of megakaryocytes in BM (thrombopoiesis)
- mediated by thrombopoietin
- circulate for 5-9d (most spp)
7
Q
Describe PLT structure
A
- OM contains Rs for adhesion and aggregation
- contain cytoskeleton with actin and myosin that allows for shape change
- contain membrane bound granules (alpha granules are red and contain vWF, fibrinogen an factors 5 and 8.. Dense granules contain ADP and Ca)
8
Q
Describe PLT surface receptors
A
- Gps associated with PLT membrane
- GP1b binds vWF
- GP2b3a binds fibrinogen on adjacent PLTs and allows PLTs to aggregate
- defects in Rs lead to abnormal PLT function and clot formation
9
Q
Stages of haemostasis
A
- PRIMARY: formation of primary PLT plug
- SECONDARY: activation of coagulation cascade and generation of insoluble fibrin which stabilises the PLT plug
- FIBRINOLYSIS: breakdown of fibrin and PLT plug
10
Q
Steps in primary haemostasis
A
- damage to endothelium and exposure of subendothelial collagen
- vWF released from damaged endothelium
- PLT adhesion occurs
- PLTs bind to collagen via R GP1b and vWF from endothelium
- once PLTs have adhered to collagen, they undergo shape change and become spherical with filipodia
- additional receptors for vWF (GP1b) and fibrinogen (GP2b3a) are exposed
11
Q
Describe PLT aggregation
A
- PLTs bind fibrinogen via GP2b3a
- this occurs b/w adjacent PLTs thereby forming a clump/aggregate of PLTs
- fibrinogen is generated from the coagulation cascade, it is released from PLTs and found in plasma
12
Q
Describe PLT secretion
A
- aggregating PLTs rapidly degranulate
- release of ADP, fibrinogen, vWF
- Thromboxane A2 also released from PLT membrane
- these all increase PLT adhesion and aggregation
- PLTs also release factors 5 and 8 which are involved in coagulation
13
Q
Describe secondary haemostasis
A
- involves activation of coagulation cascade
- soluble enzymes (serine proteases) found in circulation
- each step of coagulation cascade converts one of these factors from an inactive stage (proenzyme) to its active state
- each step amplifies the system
- end result is the formation of insoluble fibrin
- fibrin stabilises the primary PLT plug
14
Q
Outline the coagulation cascade
A
- divided into intrinsic, extrinsic, common pathways
- done to facilitate lab tests
- division doesn’t exist in vivo
15
Q
Describe the extrinsic system (initiation)
A
- most important in vivo
- tissue factor (TF) released from damaged tissue binds to and activates F8 in presence of Ca
- TF-F8 complex activates F5 of the common pathway and F9 of the intrinsic pathway
16
Q
Describe the intrinsic pathway (amplification)
A
- F7 is activated by contact with a negatively charged surface (cofactor HMWK)
- activated F8 cleaves and activates F11 which in turn activates F9 (calcium required)
- activated F9 in turn activates F10 of the common pathway (calcium required)
17
Q
Describe the common pathway
A
- starts with activation of factor 10
- activated F10 binds activated F5 and calcium on PLT surface
- this complex converts prothrombin (F2) to thrombin (F2a)
- thrombin converts fibrinogen (F1) to fibrin (F1a)
- fibrin crosslinked by activated F13
18
Q
What are inhibitors of coagulation?
A
- Antithrombin 3: inhibits thrombin and activated F10
- Activity of AT3 increased by heparin from endothelium
- Protein C: inactivates factors 5 and 8
19
Q
Outline fibrinolysis
A
- enzymatic breakdown of fibrin by plasmin
- plasmin is derived from plasminogen found in PLT membrane and plasma
- plasmin degrade to both fibrinogen and fibrin to produce Fibrin Degradation Products (FDPs)
20
Q
Describe lab evaluation of PLTs by PLT concentration
A
- automated counts can be done on PLTs collected into EDTA as part of CBC
- good accuracy for all spp except cat/sheep/ goat d/t overlap b/w RBC and PLT size (i.e. small RBCs)
- PLT clumps also cause inaccurate counts d/t lack of even distribution and d/t overlap in size b/w clumps and RBCs (v. common in cats)
- can also estimate PLT count by SMEAR. Must be done in cats and CKCS as latter often thrombocytopaenic with giant PLTs which may be counted as RBCs d/t large size
21
Q
Describe interpretation of PLT numbers
A
- upper reference limit (>1000*1069/L) are consistent with THROMBOCYTOSIS and may be associated with increased risk of thrombosis
22
Q
What does buccal mucosal bleeding time assess?
A
- PLTs function (not number)
- measures length of time for PLT plug to form: evaluates primary haemostasis and PLT function
- use spring loaded cassette to make small incision into buccal mucosa and blood is blotted until bleeding stops
- v low sensitivity
- INCREASED: if thrombocytopaenia, vWF dz, disorders of PLT function. Will NOT be increased with coagulation deficiencies
23
Q
Name 3 disorders of PLTs
A
- thrombcytopaenia
- thrombocytosis
- disorders of PLT function
24
Q
What can PLT disorders lead to?
A
- haemorrhage if PLT numbers are decreased or function is impaired. typically seen as ecchymoses or petechiae
- can lead to increased risk of thrombosis if numbers increased
25
Thrombocytopaenia mechanisms
- INCREASED PLT DESTRUCTION OR CONSUMPTION: immune-mediated, haemorrhage, DIC, sequestration
- DECREASED PRODUCTION (BM problem)
- INFECTIOUS: numerous causes
26
Outline immune-mediated thrombocytopaenia (IMTP)
- commonest cause of thrombocytopaenia
| - PLT numbers often v low
27
What is Evan's syndrome?
concurrent immune-mediated thrombocytopaenia and anaemia
28
How are RBCs normally destroyed?
Majority destroyed in periphery, subset can be destroyed by megakaryocytes
29
Types of IMTP
- PRIMARY: Abs are produced against PLT antigens
| - SECONDRAY: other immune dz (SLE), drugs/vaccine / injection, neoplasia, infectious
30
CS - IMTP
- profound thrombocytopaenia (always recheck #s, look for clumps on smear and clots in tube)
- evidence of petechial or ecchymotic haemorrhages
- Hx of bleeding from gums, mucosal surfaces, prolonged bleeding from wounds etc
31
Dx - IMTP
- difficult to confirm as dx of exclusion
- may see megakaryocyte hyerplasia (BM)
- BM exam can be done even if PLT #s v low - animals rarely bleed from this site
- Anti-platelet Ab - need large volumes of blood as PLT #s will be low
- response to tx
32
Causes - thrombocytopaenia
- INCREASED CONSUMPTION
- SEQUESTRATION
- DECREASED PRODUCTION
- INFECTION
33
Outline increased consumption as cause of thrombocytopaenia
- haemorrhage: #s shouldn't be lower than 100*10^9/L
- DIC: #s may be v low
- usually with DIC there will be other signs of a coagulation defect
- check PT, PTT - prolonged
- check FDPs - decreased
34
Outline sequestration as a cause of thrombocytopaenia
Rare but may occur with splenomegaly or with large cavitated mass
35
Outline decreased production as a cause of thrombocytopaenia
- BM dz
- neoplasia
- drugs
36
Outline infectious causes of thrombocytopaenia
- number of causes possible including immune-mediated and decreased production: FeLV, BVD, Ehrlichia, Leishmania
37
List some disorders of PLT function
- Glanzmann's thrombocytopaenia - defect in GP2b3a
- Canine thrombopathia - abnormal GP2b3a exposure and impaired degranulation
- Bovine thrombopathia - defect not known
38
Describe Glanzmann's thrombocytopaenia
- defect in GP2b3a
- otterhounds and Great Pyrenees
- Quarter horse
- defective PLT aggegation and abnormal clot retraction
39
Describe canine thrombopathia
- abnormal GP2b3a exposure and impaired degranulation
| - Basset hounds
40
Describe bovine thrombopathia
- defect not known
- simmentals
- mild to severe bleeding
41
3 broad causes of thrombocytosis
- physiological (tx)
- reactive (secondary)
- essential thrombocythemia
42
What can cause transient physiological thrombocytosis?
epinephrine induced splenic contraction
43
Describe reactive (secondary) thrombocytosis
- increased thrombopoeitin and possibly IL-6
| - inflammation, haemorrhage, iron deficiency
44
Outline essential thrombocythemia
- PLT equivalent of leukaemia
- myeloproliferative disorder
- marked persistent increase in PLTs
- BM megakaryocytes increased and may have abnormal morphology
- function variable - may see petechiae and ecchymoses or thrombosis
- TPO levels normal or increased
45
Describe von Willebrand's disease
- vWF is a plasma GP needed for PLT adherence to collagen and formation of primary haemostatic plug
- synthesised by endothelial cells, PLTs and megakaryocytes- circulates bound to F8 (protective function of F8)
- may see concurrent decrease in F8
- exists in small, medium and large multimers: large multimers are the most active in haemostasis
- common in dogs, rare in cats/horses
- 3 types
46
CS - von Willebrand's disease
- mucosal bleeding (GIT, epistaxis, haematuria)
- bleeding may be absent
- no petechiae (differentiate it from other PLT disorders)
- see prolonged buccal mucosal bleeding time w/o thrombocytopaenia
- clotting times usually normal but PTT may be prolonged d/t decrease in F8
-
47
Type 1 von Willebrand's disease
- ALL multimers present but at decreased concentrations
| - variable severity of bleeding but not until concentration of vWF are
48
Type 2 von Willebrand's disease
- qualitative abnormalities in vWF structure and function
- often disproportionate decrease in large multimers
- severe and uncommon
- seen in german shorthaired and wirehaired pointers, one horse case
- autosomal recessive
49
Type 3 von Willebrand's disease
absence of all vWF multimers
50
Tests/Dx for von Willebrand's disease
- measure levels of vWF Ag
- collect blood into EDTA or citrate (for latter, ensure blood: citrate ratio of 1:9)
- vWF levels will be decreased by clots in the sample and by hemolysis but are unaffected by lipemia
- separate plasma immediately, freeze and ship with ice
* ELISA: quantitative measurement of vWF using species specific Abs,
51
Interpretation of vWF ELISA
-
52
Tx - vWD
- transfusion to supply vWF
- CRYOPRECIPITATE best as concentration of vWF 5-10 times greater than plasma, give 1 IU/10kg
- PLASMA at 6-12ml/kg if cryoprecipitate not available
- whole blood if animal is anemic
- desmopressin (DDAVO) as preop prophylaxis for dogs with type 1, causes release of vWF from endothelium, give 1microg/kg SC 30 min prior to sx, also an IN preparation available
53
Outline sample collection for lab evaluation of coagulation
- citrated plasma (most tests)
- ratio of anticoagulant: blood should be 1:9 (fill to line), always check for clots
- don't sample through herparinised catheters
- minimise trauma when collecting blood otherwise will activate PLTs and coagulation
- centrifuge to separate plasma within 1hr
- analyse within 4 hrs or freeze plasma
- always include a spp specific control
54
Describe the ACT test
- Activated Clotting Time
- evaluates intrinsic and common pathways
- collect 2ml whole blood into ACT tube containing diatomaceous earth
- incubate for 60s at 37 degrees and check for clots every 5-10s
- time to initial signs of clot is the ACT (s)
- interpretation similar to PTT but less sensitive
- will be prolonged with thrombocytopaenia
55
Describe the PTT test
= Partial Thromboplastin Time
- screening test for intrinsic and common pathways
- incubate citrated plasma with excess phospholipid, contact activator and calcium
- measure time to formation of clot
- lipemia, hemolysis, oxyglobin tx and icterus interfere with clot formation
56
Explain PTT interpretation
- prolonged PTT indicates defect in intrinsic factors (12, 11, 9 and 8) or common pathways (F10, 5, 2 and fibrinogen)
- factor activity must be
57
Describe the PT test
- prothrombin time
- screening for defects in extrinsic and common pathways
- incubate citrated plasma with tissue thromboplastin (TF) and calcium
- measure time to clot formation
58
Explain PT interpretation
- prolonged PT indicates defect in extrinsic (factor 7) or common pathways of coagulation
- Factor activity must be
59
Which coagulation tests measure intrinsic and common pathways?
PTT and ACT
60
Which coagulation test measures the extrinsic and common pathways?
PT
61
What are other coagulation tests?
- specific factor analysis
- to detect specific factor deficiencies
- usually done to detect hereditary deficiencies
- done by correcting PT and PTT of test plasma with normal plasma
62
What are tests of fibrinolysis?
= FDPs
- use latex agglutination test
- special test and kit requires specialised tubes so lab needs to be contacted
- done on serum (needs to be separated within 30 minutes)
- test immediately or freeze
- INCREASED FDPs: with DIC
- not specific
- may also increase with haemorrhage, jugular vein thrombosis (horse) and liver disease
* D-dimers: plasmin mediated degradation of cross-linked fibrin, detects fibrinolysis after fibrin cross-linking
63
Examples - disorders of coagulation
- acquired factor deficiencies
- main one is the result of vit K deficiency
- typically with rodenticide toxicity (coumarin, indanedione) or sweet clover ingestion (cattle)
- vit K dependent factors are factors 2, 7, 9 and 10.
64
Outline mechanism of vit K deficiency
- factors 2, 7, 9 and 10 are produced in liver
- are activated by vit K dependent carboxylase: this step requires reduced vit K
- production of reduced vit K requires action of vit K reductase
- vit K reductase inhibited by coumarin type rodenticides
- leads to lack of active factors 2, 7, 9 and 10 and a coagulopathy
- extrinsic, intrinsic and common pathways affected
- factor 7 has shortest half life so will decrease first
- PT is often prolonged 1st in early vit K deficiency
65
CS and tests for vit K deficiency
- CS: haemorrhage (thorax, abdomen),
- TEST: elevated PT and PTT
- PLT numbers and buccal mucosal bleeding time should be normal but mild thrombocytopaenia possible (d/t consumption associated with haemorrhage)
- FDPs may be elevated
- will see same results if animal has coagulopathy secondary to hepatic dz
66
Tx - vit K deficiency
- emetics, cathartics, activated charcoal if ingestion of rodenticide recent
- transfusions of WFB or FFP to replace coagulation factors
- may also need PRBCs to severe anaemia
- Vit K deficiency: use vit K1 orally or PN, can give loading dose SC followed by lower dose divided q 8hrs, same dose can be given orally with a fatty meal, may take 12 hours before vit K therapy will shorten PT and decrease bleeding
67
How long do you need to tx for vit K deficiency?
- Warfarin or other 1st generation rodenticide; 1 week
- 2nd/ 3rd generation rodeniticides used: need to tx for at least 3 wks, often up to 6 wks
- check PT 24-48 hrs after last dose, if prolonged reinstate tx for another 2 wks and recheck PT
68
Examples - hereditary defect of coagulation
- F7 deficiency
- Haemophilia A (F8 deficiency)
- Haemophilia B (F4 deficiency)
- F11 deficiency
- F12 deficiency
69
Tx - inherited coagulation defects
- transfusions of FWB or plasma to replace factor deficiency and red cells
- use of fresh or frozen plasma will give a small amount of factor
- cryoprecipitate: 10x more factor 8 than plasma
70
What is D.I.C.?
= disseminated intravascular coagulation
- mixed haemostatic defect
- results when excessive coagulation leads to widespread thrombosis
- haemorrhage eventually results as all coagulation factors are consumed
- not a primary event but secondary to other underlying disease (neoplasia, liver disease, I-M dz, infectious dz)
- acute or chronic
71
What are the haemostatic abnormalities with D.I.C.?
* thrombocytopaenia (almost always)
* prolonged PT and TT (commonly)
- elevated FDPs
- decreased fibrinogen
- decreased AT3
72
Tx - D.I.C.
- stop coagulation process
- heparin (different regimens)
- transfusion of whole blood, plasma or cryoprecipitate as source of AT3
- aspirin to stop PLT activation
- correct other unerlying abnormalities
73
Px - D.I.C.
Poor
74
Summarise the general approach to the bleeding patient
- PLT defect likely if haemorrhages are ecchymotic or petechiall
- if not - coagulation defect (consider age, if v young hereditary possible, hx of toxin exposure)
- Check CBC (PLT #)
- evaluate HCT and PLT #s
75
Summarise approach to bleeding patient if thrombocytopaenia is present
- check for clots, check smear, recheck #s
- assess degree of TP
- PLTs approx 100*10^9/L consider haemorrhage as a cause
- PLTs
76
What should you consider if PLT #s are WNL but haemorrhages or has ecchymosis/ petechiae?
- consider vWD (haemorrhages)
- consider PLT function defects (ecchymosis or petechiae)
- if possible check BMBT (buccal mucosa bleeding time)
- assay for vWF Ag
- check clotting function (PTT may be increased d/t concurrent decrease in factor 8)
77
What to do if PT and PTT are prolonged?
- consider vit K deficiency or DIC
78
What if PTT is prolonged alone?
consider defects of intrinsic pathways (haemophilia A and B)
79
What if PT is prolonged alone?
consider early vit K deficiency, liver dz, early DIC
