Blood coagulation, Haemostasis, and its Investigation

Question 1

Haemostasis - define

Answer 1

Protective process evolved in order to maintain a stable physiology

“An explosive reaction designed to curtail blood loss, restore vascular integrity and ultimately preserve life”

Question 2

The Horseshoe Crab - define

Answer 2

Limulus Polyphemus

‘A primitive coagulation pathway can be initiated by endotoxin’

Question 3

The Haemolymph contains what

Answer 3

The Haemolymph contains amebocytes:

Proteins of the coagulation system
Proteins & peptides of the immune system

Question 4

Haemostasis - life preserving processes = describe

Answer 4

Life preserving processes designed to maintain blood flow
Respond to tissue injury
Curtail blood loss
Restore vascular integrity & promote healing
Limit infection

Question 5

Haemostasis - 4 components

Answer 5

Four Key Components
Endothelium
Coagulation
Platelets
Fibrinolysis

Question 6

What makes a Blood Clot?

Answer 6

Fibrin mesh
Platelets
Red blood cells

Question 7

Coagulation - decribe process briefly

Answer 7

Vessel damage
& Blood loss

Vascular spasm

Platelet Plug forms

Coagulation

Question 8

Primary haemostasis - description

Answer 8

Primary haemostasis:
Vasoconstriction (immediate)
Platelet adhesion (within seconds)
Platelet aggregation and contraction (within minutes)

Question 9

Secondary haemostasis - description

Answer 9

Secondary haemostasis:
Activation of coagulation factors (within seconds)
Formation of fibrin (within minutes)

Question 10

Fibrinolysis - description

Answer 10

Fibrinolysis:
Activation of fibrinolysis (within minutes)
Lysis of the plug (within hours)

Question 11

Clot strength in terms of stages

Answer 11

Initiation = slow rise ~ 0
Amplification = rapid increase
Stable clot = strongest
Lysis = steady decrease to 0

Question 12

Characteristic of heamostasis at rest

Answer 12

Haemostasis at rest: triggers and cofactors separated

Question 13

vWF function under shear forces

Answer 13

Under shear forces, self-association of plasma VWF occurs surface of platelets + endothelial cells = creating fibrillar structures that further facilitate platelet adhesion

Question 14

Platelet aggregation function

Answer 14

Prevents excessive blood loss at site of injury

Question 15

When does seconday haemostasis take place

Answer 15

This plug of activated platelets, localised to the site of injury, provides the phospholipid surface upon which Secondary Haemostasis takes place

Question 16

When does primary haemostasis take place

Answer 16

Primary hemostasis = when platelets attach to damaged endothelium, adhesion allows the platelets to undergo a shape change = aggregation
Once adhered to each other a temporary platelet plug is created

Question 17

Brief process of haemostatic plug formation

Answer 17

Vessel constriction
Formation of an unstable platelet plug
platelet adhesion
platelet aggregation
(above is primary haemostasis)
Stabilisation of the plug with fibrin blood coagulation (secondary)
Dissolution of clot and vessel repair fibrinolysis

Question 18

Fibrin mesh function

Answer 18

Fibrin mesh binds and stabilises platelet plug and other cells

Question 19

Fibrinogen (I) function

Answer 19

Forms clot (fibrin)

Question 20

Prothrombin (II) function

Answer 20

Its active form (IIa) activates I, V, VII, XIII, protein C, platelets

Question 21

Tissue factor (III) function

Answer 21

Co-factor of VIIa

Question 22

V (proaccelerin, labile factor)

function

Answer 22

Co-factor of X with which it forms the prothrombinase complex

Question 23

VI function

Answer 23

Unassigned - old name of Factor Va

Question 24

VII (stable factor) function

Answer 24

Activates IX, X

Question 25

VIII (antihaemophilic factor) | function

Answer 25

Co-factor of IX with which it forms the tenase complex

Question 26

IX (Christmas factor) | function

Answer 26

Activates X: forms tenase complex with factor VIII

Question 27

X (Stuart-Prower factor) | function

Answer 27

Activates II: forms prothrombinase complex with factor V

Question 28

XI (plasma thromboplastin antecedent) | function

Answer 28

Activates XII, IX and prekallikrein

Question 29

XII (Hageman factor) | function

Answer 29

Activates prekallikrein and fibrinolysis

Question 30

XIII (fibrin-stabilizing factor) | function

Answer 30

Crosslinks fibrin

Question 31

von Willebrand factor | function

Answer 31

Binds to VIII, mediates platelet adhesion

Question 32

FVII deficiency effect

Answer 32

FVII deficiency causes bleeding

Question 33

FXII deficiency effect

Answer 33

FXII deficiency not associated with bleeding

Question 34

What does each action in waterfall hypothesis require

Answer 34

Each reaction requires: Ca2+ Phospholipid ± Specific co-factors

Question 35

Describe clotting cascade

Answer 35

TF is outside the lumen Formation of TF-FVIIa complex Recruitment of FX and formation of thrombin

Question 36

Fibrinolysis (clot dissolution) function

Answer 36

Main function: clot limiting mechanism repair and healing mechanism

Question 37

Fibrinolysis (clot dissolution) - characteristic of the process

Answer 37

Series of tightly regulated enzymatic steps | - feedback potentiation & inhibition

Question 38

Fibrinolysis (clot dissolution) - key players

Answer 38

Main Key players: Plasminogen Tissue plasminogen activator (t-PA) & urokinase (u-PA) Plasminogen activator inhibitor -1 and -2 α2-plasmin inhibitor

Question 39

Formation of plasmin - describe

Answer 39

Plasminogen → plasmin through tissue plasminogen activator, tPA

Question 40

Formation of plasmin - effect

Answer 40

D dimers are generated when cross-linked fibrin is degraded. | FDP (Fibrin degradation products) are generated if non-cross linked fibrin or fibrinogen is broken down.

Question 41

Uses of tPA and streptokinase

Answer 41

tPA and a bacterial activator, streptokinase, are used in therapeutic thrombolysis for myocardial infarction (Clot busters)

Question 42

Describe haemostasis and thrombosis in relation to one another

Answer 42

Haemostasis and Thrombosis: a Balance Normal haemostasis: a state of equilibrium Fibrinolytic factors, anticoagulant proteins VS Coagulation factors, platelets

Question 43

Cuase of thrombosis

Answer 43

↑ Coagulation factors, platelets and ↓ Fibrinolytic factors, anticoagulant proteins

Question 44

Chronic venous insufficiency effects

Answer 44

Atrophic changes Hyperpigmentation Ulceration Infection

Question 45

Cause of bleeding

Answer 45

↑ Fibrinolytic factors, Anticoagulant proteins and ↓ Coagulation factors, Platelets

Question 46

Define ecchymosis

Answer 46

Easy bruising (ecchymosis) = a discoloration of the skin resulting from bleeding underneath, typically caused by bruising Virtually all bleeding disorders and often in normals

Question 47

Principles of clotting tests

Answer 47

Incubate plasma with reagents necessary for coagulation: Phospholipid, co-factors Trigger or activator Calcium Measure time taken to form fibrin clot

Question 48

Prothrombin time (PT) - define and describe characteristics

Answer 48

Prothrombin time (PT) is a blood test that measures how long it takes blood to clot Sensitive to extrinsic pathway and to a lesser extent common pathway TF driven

Question 49

APTT (Activated Partial Thromboplastin Time) - define and describe characteristics

Answer 49

The partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT or APTT) is a blood test that characterizes coagulation of the blood Sensitive to intrinsic pathway and to a lesser extent common pathway Contact activated

Question 50

TT (Thrombin Time) - define and describe characteristics

Answer 50

Thrombin time (TT), a blood test that measures the time it takes for a clot to form in the plasma of a blood sample containing anticoagulant, after an excess of thrombin has been added. Sensitive to defects in conversion of fibrinogen to fibrin

Question 51

Overview of Coagulation Pathways

Answer 51

Activated partial thromboplastin time (APTT) = 1. Surface activating agent (e.g. kaolin) 2. Phospholipid 3. Calcium = Intrinsic pathway PT = 1. Thromboplastin Tissue factor Phospholipid 2. Calcium = Extrinsic pathway both feed into Thrombin time = thrombin = common pathway All combining to form = fibrin clot

Question 52

Accuracy of haemostasis laboratory tests depends on what

Answer 52

Accuracy of haemostasis laboratory tests depends on the quality of the specimen submitted

Question 53

Effect of under filling the tube

Answer 53

Under filling the tube yields grossly inaccurate results.

Question 54

Problems with blue-top tube = pre-analytical error

Answer 54

Partial fill tubes | Vacuum leak and citrate evaporation

Question 55

Problems with phlebotomy = pre-analytical error

Answer 55

(using a needle to take blood from a vein) ``` Heparin contamination Wrong label Slow fill Underfill Vigorous shaking Difficult venepuncture ```

Question 56

Laboratory errors = pre-analytical error

Answer 56

Delay in testing Prolonged incubation at 37°C Freeze/thaw deterioration

Question 57

Biological effects that are pre-analytical errors

Answer 57

Hct ≥55 or ≤15 | Lipaemia, hyperbilirubinaemia, haemolysis

Question 58

Mixing studies - describe

Answer 58

Mix patient and normal plasma in equal volumes (50:50 mix) Repeat abnormal coagulation test Test normalises – factor deficiencies Test remains abnormal – inhibitor (usually antibody)

Question 59

What tests do you do if you obtain an normal PT + abnormal APTT, include results

Answer 59

Repeat at 50:50 mix If 50:50 abnormal: Test for inhibitor activity: Specific factors: VIII,IX, XI Non-specific (anti-phospholipid Ab) If 50:50 mix normal Test for factor deficiency: Isolated deficiency in intrinsic pathway (factors VIII, IX, XI) Multiple factor deficiencies (rare)

Question 60

What tests do you do if you obtain an abnormal PT + normal APTT, include results

Answer 60

Repeat at 50:50 mix If 50:50 abnormal: Test for inhibitor activity: Specific: Factor VII (rare) Non-specific: Anti-phospholipid (rare) If 50:50 mix normal: Test for factor deficiency: Isolated deficiency of factor VII (rare) Multiple factor deficiencies (common) (Liver disease, vitamin K deficiency, warfarin, DIC)

Question 61

What tests do you do if you obtain an abnormal PT + abnormal APTT, include results

Answer 61

Repeat at 50:50 mix If 50:50 abnormal: Test for inhibitor activity: Specific : Factors V, X, II, I (rare) Non-specific: anti-phospholipid (common) If 50:50 mix normal: Test for factor deficiency: Isolated deficiency in common pathway: Factors V, X, Prothrombin, Fibrinogen Multiple factor deficiencies (common) (Liver disease, vitamin K deficiency, warfarin, DIC)

Question 62

What tests do you do if you obtain an abnormal PT + abnormal APTT, include results

Answer 62

Repeat a normal test ``` If abnormal: Dysfibrinogenaemia Abnormal fibrinolysis (e.g. α2 anti-plasmin def) Elevated FDPs ``` ``` If normal: Von Willebrand’s disease Platelet disorder FXIII deficiency Non-coagulation defect (e.g. vascular disorder) ```

Question 63

D-dimer Testing - characteristics

Answer 63

A measure of the D-dimer, a fibrin degradation product Found elevated in the situation of enhanced fibrinolysis (Thrombosis, DIC) Not specific for thrombosis also elevated as an acute phase reactant A Negative result is useful if clinical suspicion of VTE is low