Blood Coagulation,Haemostasis and its investigation Flashcards
1
Q
- What is haemostasis?
A
o Protective process evolved in order to maintain a stable physiology.
o “An explosive reaction designed to curtail blood loss, restore vascular integrity and ultimately preserve life”.
2
Q
- What is an initiator of haemostasis
A
Infection
3
Q
- What is an endotoxin and what can it initiate?
A
Endotoxins are basically pyrogens found in gram- bacteria cell walls
They can initiate a primitive coagulation pathway
4
Q
- What is the haemolymph?
A
Its basically the fluid equivalent of blood in most inverter-brae animals eg horseshoe crab
Contains proteins of the coagulation system as well as proteins/peptides of the immune system
5
Q
- The haemolymph contains amebocytes- what do they do?
A
Amebocytes are mobile cells - they allow the infection to be contained to stop access to other vital organs
6
Q
- What is Disseminated intravascular coagulation (DIC)?
A
condition in which small blood clots develop throughout the bloodstream, blocking small blood vessels.
7
Q
- Explain the appearance of DIC?
A
Looks like small blood spots under the skin
8
Q
- What are the four key concepts in haemostasis?
A
- Endothelium
- Coagulation
- Platelets
- Fibrinolysis
9
Q
- What makes a blood clot?
A
Fibrin Mesh
Platelets
RBC’s
10
Q
- What is a haemostasis overview in 4 steps?
A
-Vessel Damage and Blood loss -Vascular Spasm -Platelet Plug Forms -Coagulation
11
Q
- We can break the haemostatic system into 3 phases:
What does the phase “Primary Haemostasis”
include and give a time frame for each step:
A
- Vasoconstriction (immediate)
- Platelet adhesion (within seconds)
- Platelet aggregation and contraction (within minutes)
12
Q
- We can break the haemostatic system down into 3 phases:
What does the phase “ Secondary Haemostasis” include and give a time frame for each step:
A
Activation of coagulation factors (within seconds)
Formation of fibrin (within minutes)
13
Q
- We can break the haemostatic system down into 3 phases:
What does the phase “ Fibrinolysis” include and give a time frame for each step?
A
Activation of fibrinolysis (within minutes)
Lysis of the plug (within hours)
14
Q
- What is Von Willebrand factor?
A
Multi-meric structure that becomes unravelled and active upon sheer stress. It acts as an anchor for platelets allowing their adhesion
15
Q
- What activates Von Willebrand factor?
A
When tissue damage exposes the endothelium to tissue factor, it causes von Willebrand factor to become activated.
16
Q
- What is the aim of a ‘platelet plug’ ?
A
Platelet Aggregation —> Platelet Plug —-> Prevents excessive blood loss at the injury site
17
Q
- What activates the coagulation process?
A
vWF Activation —> Platelet Adhesion to exposed endothelium wall
Exposed TF –> Production of small amount of thrombin
-> Activates Coagulation process
18
Q
- What is the role of platelets in coagulation process within primary haemostasis?
A
Activation:
- Thrombin activates platelets
Aggregation:
-Platelets release more attractant chemicals to attract more platelets
Contraction:
- Activated Platelets –> Conformational change –> Contract —> Form a dense plug–> Provides phospholipid surface for secondary haemostasis to take place
19
Q
- Where is the majority of coagulation factors produced in?
A
The Liver
20
Q
- What is the function of fibrinogen?
A
Forms clot (Fibrin)
21
Q
- What is the function of Prothrombin(II) ?
A
In its active form (IIa) it activates I,V,VII,XIII,Protein C and Platelets
22
Q
- What is the function of tissue factor?
A
Co-factor of Vlla
23
Q
- What in the function of Von Willebrand factor?
A
Binds to Vlla
Mediates Platelet Adhesion
24
Q
- Which deficiency causes bleeding:
-FVII deficiency
OR
-FXII deficiency
A
FVII causes bleeding bro
FXII is not associated with bleeding
25
25. What does each reaction in the waterfall cascade thing require?
Ca2+
Phospholipid
+ or - Specific Co-Factors
26
26. What activates the whole cascade?
o Extrinsic tissue damage :
Factor 7 combines with Tissue Factor forming a complex that activates other proteins in the cascade.
• Measured with prothrombin time.
27
27. What is the REVISED Initiation process of the cell-based model of coagulation?
```
o TF (outside the lumen normally) forms a TF-FVIIa complex.
o This then recruits FX and FV to the exposed endothelial, these form small quantities of thrombin.
o Thrombin activates platelets and other plasma-borne factors e.g. FVIII and FIX.
```
28
28. What is the amplification process of the cell-based model of coagulation?
These factors enable FX and FV to bind to platelet surfaces which leads to a thrombin burst.
29
29. What is the propagation process of the cell-based model of coagulation?
oThrombin burst then allows for large-scale production of fibrin which is needed for a clot.
30
30. What is the whole process of cell-based model of coagulation?
o TF (outside the lumen normally) forms a TF-FVIIa complex.
o This then recruits FX and FV to the exposed endothelial, these form small quantities of thrombin.
o Thrombin activates platelets and other plasma-borne factors e.g. FVIII and FIX.
o These factors enable FX and FV to bind to platelet surfaces which leads to a thrombin burst.
o Thrombin burst then allows for large-scale production of fibrin which is needed for a clot.
31
31. What is fibrinolysis?
o Series of tightly regulated enzymatic steps: Feedback potentiation & inhibition
32
32. What is the main function of fibrinolysis?
clot limiting mechanism and repair and healing mechanism.
33
33. What 5 key things do you need for fibrinolysis to take place?
```
• Plasminogen,
• Tissue plasminogen
activator (t-PA) &
urokinase (u-PA)
• Plasminogen activator
inhibitor -1 and -2
• α2-plasmin inhibitor
```
34
34. What is the process of fibrinolysis?
o Plasminogen is converted into plasmin by tissue plasminogen activator, tPA.
o Plasmin forms a cross-linked fibrin clot.
o Cross-linked fibrin clot degradation: D dimers.
o Non crosslinked fibrin/fibrinogen degradation: Fibrin Degradation Products (FDP).
o tPA and streptokinase (bacterial activator) are used in therapeutic thrombolysis for myocardial infarction (clot busters).
35
35. What does normal haemostasis have a balance between?
Haemostasis (Fibrinolytic Factors , anticoagulant proteins) and thrombosis (coagulation factors, platelets)
36
36. What is thrombosis?
Formation of blood clot- increase coagulation factors and platelets (decrease fibrinolytic factors and anticoagulant proteins)
37
37. What is chronic venous insufficiency?
condition that occurs when the venous wall in the leg veins are not working effectively
CVI causes blood to “pool” or collect in these veins,
38
38. What are some symptoms of Chronic Venous Insufficiency?
Atrophic changes (degenerative)
Hyperpigmentation
Ulceration
Infection
39
39. What happens if the normal haemostasis balance tips so that there is an increase in fibrinolytic factors and anticoagulant proteins?
Increased Bleeding
40
40. What is Ecchymosis?
- Easy bruising from blood under the skin
| - Present in virtually all bleeding disorders and often in normal
41
41. To test why a patient has excessive bleeding
| May do a FBC and blood film, what does this count and what can this test for?
Tells us:
- Platelet Count
- Platelet Morphology
Tests for:
-Thrombocytopenia (platelet deficiency) eg ITP or DIC
42
42. To test why a patient has excessive bleeding we
| may do coagulation tests what does this count and what can this test for?
Tells us:
- Prothrombin Time (PT)
- APTT/KCCT - activated partial thromboplastin time
- Thrombin Time (TT)
- Mixing studies
- Factor Assays
Tests for:
- Extrinsic and Intrinsic pathway
- Common pathway
- Fibrin Formation
43
43. to test why a patient has excessive bleeding we
| may do platelet function tests what does this count and what can this test for?
Tells us:
Von Willebrand factor
Platelet function analyser (PFA-100)
Platelet aggregometry(how quickly platelets aggregate)
Detects:
Platelet defects
Von Willebrand disease
44
44. What are two global tests for bleeding?
Thromboelastography (tests coagulation efficiency).
| Thrombin generation
45
45. What is the principle of clotting tests?
o Incubate plasma with reagents necessary for coagulation.
• Phospholipid, co-factors e.g. calcium, trigger or activator.
o Measure time taken to form fibrin clot.
46
46. What is prothrombin time? What is sensitive to?
PT= Time for blood to clot
Sensitive to EXTRINSIC pathway ( lesser extent to common pathway)
Tissue factor driven
47
47. What is Activated Partial Thromboplastin Time (APTT) sensitive to?
o Sensitive to intrinsic pathway and to a lesser extent common pathway.
o Contact activated.
48
48. What is Thrombin Time (TT) sensitive to?
o Sensitive to defects in conversion of fibrinogen to fibrin.
49
49. Explain a brief overview of the coagulation pathways?
You have the intrinsic pathway (affect APTT) and the Extrinsic pathway (affect PT), these both lead into the Common pathway (Affect Thrombin time) which results in a fibrin clot
50
50. What is one disadvantage of tests that tell us about clotting time?
-NO info on the amplification or lysis process
51
51. Why is it important that testing is done correctly- how do we ensure it is done correctly?
-> Needs to be done correctly = Reliable results
- > Correctly labelled for identification
- > Selected/tested in the proper order and time
52
52. The accuracy of haemostasis laboratory tests depends on quality of the specimen:
- What % of sodium citrate is blood anti coagulated with?
- What is the proportion of blood and anti-coagulant in the testing tube?
3.2% (0.109M) Sodium Citrate
Most tubes contain 0.3mL anticoagulant -for 2.7 mLs of blood
53
53. What is the consequence of under filling the tube?
-Grossly inaccurate Tubes
54
54. What are 4 types of pre-analytical errors:
1. Problems with blue-top tube
2. Laboratory Errors
3. Biological Effects
4. Problems with Phlebotomy (surgical opening on vein)
55
55. What could go wrong the blue-top tube?
- Tubes are filled partially
- Citrate Evaporates
- Vacuum leak
56
56. What biological effects could cause pre-analytical errors?
Hct (RBC count) is either >55 or <15
- Lipaemia (presence of high emulsified fat in blood)
- hyperbilirubinaemia
- haemolysis ( rupture of RBC)
57
57. What laboratory errors could there be?
- Delay in testing = prolonged incubation at 37 degrees celsius
- Freeze/thaw deterioration
58
58. What kind of problems could you have with phlebotomy (opening of the vein)
- Heparin Contamination
- Wrong label
- Vigorous Shaking
- Slow fill/ underfill
- Difficult Venipuncture
59
59. Compare manual coagulation to automatic?
Manual Coagulation = Tilt 3 times every 5sec's at 37 degrees
Automatic = Computer Used
60
60. Why would you do a mixing study?
When the clotting time is too long - test to see why its taking so long to clot, inhibitors or factor deficiencies
61
61. How does a mixing study work?
o Mix patient and normal plasma in equal volumes (50:50 mix) and repeat the abnormal coagulation test.
o If the test normalises, it shows factor deficiencies but if the test remains abnormal, it shows inhibitors such as antibodies.
62
62. What would you expect in a result where a patient with a factor deficiency did a mixing study?
so the test plasma would have a FVIII:C (activity of FVIII) of <1 (LOW) and an APTT of 95s (HIGH)
The control plasma would have a FVIII:C of 100 and APTT of 28s (NORMAL)
the 50:50 mix would have a FVIII: C of 50 and APTT of 32s
Its borderline normal-can confirm a factor deficiency
63
63. What would you expect in a result where a patient with inhibitors (like antibodies) does a mixing study?
so the test plasma WITH ANTIBODY would have a FVIII:C (activity of FVIII) of <1 (LOW) and an APTT of 95s (HIGH)
The control plasma would have a FVIII:C of 100 and APTT of 30s (NORMAL)
The mix will have a FVIII:C of 10 and APTT 75s , so still abnormal
We can confirm its an inhibitor
64
64.
Patient X , has an Abnormal PT and Abnormal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is ABNORMAL?
You would test for inhibitor activity eg
Specific ones like Factors V,X,II and I - which are rare
or
Non-Specific like anti-phospholipid which is more common
65
65.
Patient X, has an Abnormal PT and Abnormal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is NORMAL?
Test for factor deficiencies , so there might be an isolated deficiencies of one 'thing; in a common pathway eg Factors V,X prothrombin or fibrinogen
or
Multiple factor deficiencies (common) eg liver disease, vit K def, warfarin, DIC
66
66.Patient X, has an Normal PT and Normal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is NORMAL?
- Von Willebrand's disease
- Platelet Disorder
- FXII Deficiency
- Non-coagulation defect eg vascular disorder
67
67.Patient X, has an Normal PT and Normal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is ABNORMAL?
- Dysfibrinogenaemia
- Abnormal Fibrinolysis eg alpha 2 anti plasma def
- Elevated FDPs (fibrin degradation products)
68
68.Patient X, has an Normal PT and Abnormal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is ABNORMAL?
You would test for inhibitor activity eg
Specific ones like Factors V,X,II and I - which are rare
or
Non-Specific like anti-phospholipid which is more common
69
69.Patient X, has an Normal PT and Abnormal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is NORMAL?
Test for factor deficiency :
-Isolated deficiency in intrinsic pathway (factors VIII,IX and XI)
or
-Multiple Factor deficiencies (rare)
70
70.Patient X, has an Abnormal PT and Normal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is NORMAL?
Test for factor deficiencies :
-Isolated deficiency of factor VII (rare)
or
Multiple factor deficiencies (common) eg liver disease, vit K def, warfarin, DIC
71
71..Patient X, has an Abnormal PT and Normal APTT
You repeat tests with a 50:50 mix
What should you test for if the 50:50 mix is ABNORMAL?
You would test for inhibitor activity eg
-Specific ones like Factors VII - which are rare
or
Non-Specific like anti-phospholipid which is also rare
72
72. What is D Dimer?
a fibrin degradation product
73
73. When would D Dimer be elevated?
o It is found elevated in the situation of enhanced fibrinolysis (Thrombosis, Disseminated Intravascular Coagulation)
o Not specific for thrombosis also elevated as an acute phase reactant
74
74. What is a negative result of D Dimer useful for?
o A Negative result is useful if clinical suspicion of Venous Thromboembolism (VTE) is low.
