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Blood Clotting (Coagulation)
The process of blood clotting and then the subsequent
dissolving of the clot, following repair of the injured tissue,
is termed Haemostasis.
A problem with the coagulation system is called a
Coagulopathy.i.e.Depletion of a factor (absence)
Deficiency of a factor (decreased amount)
Dysfunction of a factor (not working)
John Santangelo
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Bone Marrow
John Santangelo
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Platelets
Small, granulated bodies that aggregate at the site of injury
Non-nucleated
Half-life of 4 days Count- 150 400 x 109/L of blood
Made from megakaryoblasts in Bone marrow
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Thrombopoiesis
Pluripotent stem cell
Committed stem cell
Megakaryoblast
Megakaryocyte
Platelets
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Megakaryocytes
Giant cells- 35-160m in diameter
Multinucleated
Forms 2000-4000 platelets
Platelets formed by pinching off ofcytoplasm
Megakaryocyte
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Thrombopoietin
Produced in kidney and liver
Cause megakaryocyte maturation
Bound to platelets- feedback
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Platelet morphology
Non-nucleated, Colorless disc, 2-4 m in diameter
Cell membrane: 6 nm in thickness
Phospholipids important in initiation of
Coagulation
Receptors for ADP, vWF, collagen, fibrinogen,
thrombin
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Functions of platelets
1.Hemostasis
2. Coagulation of blood
3. Clot retraction
4. Phagocytosis
5. Storage and transport- serotonin &
histamine
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Primary Haemostasis
Dependent on Platelets and Von Willebrand Factor (vWF)
Platelets gather and attach to vWF
vWF is needed for platelet adhesion
Platelets degranulate after attachment and release ADP and
Thromboxane which attracts more platelets
Forms a platelet plug
Requires endothelial damage to adhere
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Secondary Hemostasis
Platelet aggregation initiates secondary haemostasis through
the coagulation cascade
Coagulation cascade is initiated by the intrinsic or extrinsicpathway
The final cascade results in fibrin deposition cross-linking
platelets and clot formation
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Thrombocytopaenia:
A reduction in platelets below the Normal Reference Range (NRR)
Bone marrow depression
Hypersplenism
Viral infections
Idiopathic Thrombocytosis:
Splenectomy
Epinephrine administration
Unknown cause
Adrenalin
Platelet NRR = 150 400 x 109
/L
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Vivo:
Inside the body
Vitro:
Outside the body
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Thrombocytosis:
An increase in platelets above the Normal Reference Range (NRR)
Thrombocytopaenia:
A decrease in platelets below the Normal Reference Range (NRR)
Thromboasthenia:
Abnormal platelet function
Normal Reference Range for platelets:
150
400 x 109/L
Platelets are also called, Thrombocytes
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Epistaxis: Bleeding nose
Menorrhagia: Excessive bleeding during menstruation
Petechiae: Bleeding under the skin. (small red spots)
Purpura: Bleeding under the skin. (the small red spots join)
Petechiae
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Purpura
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Liver
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Femur
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The initial phase of the coagulation process is vascular constriction.
This limits the flow of blood to the area of injury.
Next, platelets become activated by thrombin and aggregate at
the site of injury, forming a temporary, loose platelet plug.
The protein fibrinogen is primarily responsible for stimulating
platelet clumping.
Platelets clump by binding to collagen that becomes exposedfollowing rupture of the endothelial lining of vessels.
Upon activation, platelets release the nucleotide, ADP and the
eicosanoid, TXA2 (both of which activate additional platelets),
serotonin, phospholipids, lipoproteins, and other proteinsimportant for the coagulation cascade. In addition to induced
secretion, activated platelets change their shape to
accommodate the formation of the plug.
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To insure stability of the initially loose platelet plug, a fibrin
mesh (also called the clot) forms and entraps the plug.
If the plug contains only platelets it is termed a white thrombus.
If red blood cells are present it is called a red thrombus.
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Finally, the clot must be dissolved in order for normal blood
flow to resume following tissue repair.
The dissolution of the clot occurs through the action of the
conversion ofplasminogen to plasmin.
Two pathways lead to the formation of a fibrin clot:
The intrinsic pathway
and
The extrinsic pathway.
These two pathways converge on a common pathway thatleads to clot formation.
Both pathways are complex and involve numerous different
proteins termed clotting factors.
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Hemostasis
Injury to vessel
Constriction of injured vessel (vasospasm)
Platelet adhesionPlatelet activation and aggregation
Temporary platelet plug formation
Activation of clotting factors
Fibrin network
True clot
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When blood is collected into a tube it clots.
It clots faster in a glass tube because of the rough surface of
the glass.
When collected into a plastic tube it takes much longer because
the plastic is has a smooth surface.
The plastic tubes are coated on the inside to promote clotting
When the skin is cut it provides a rough surface whichpromotes clotting as well as the cut tissue releasing tissue
factor.
To perform a coagulation test, unclotted blood is needed.
Coagulation test should be done within 4 hours of collection
The easiest way to stop blood clotting in the tube is to
remove one of the clotting factors.
Th i t l tti f t t it CALCIUM (F t IV)
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The easiest clotting factor to remove it CALCIUM. (Factor IV)
Note that we use Roman Numerals for the clotting factors.
The blood collected from a patient to perform Coagulation studies is
placed into a tube containing 3.8% Sodium Citrate.
Sodium Citrate is an anticoagulant
The ratio of Sodium Citrate to Whole Blood is 1:10
0.5mL Sodium Citrate + 4.5mL Whole BloodThe Citrate combines with the Calcium making it unavailable for
clotting.
Therefore the blood remains liquid.
In the laboratory, calcium is added to this blood and the time it takes
to form a clot in the plasma is measured.
Note that plasma is used to perform the test not whole blood or
Serum.
All th l ti f t d d i th Li
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All the coagulation factors are produced in the Liver
except the following:
VIII & vWF (Von Willebrand Factor )
Factors II VII IX X are Vitamin K dependent
The normal bacterial flora in the bowel (E Coli)
produces Vitamin K
It is also available from plant and animal sources
In the newborn, there is no normal bowel flora so a newborn
is often vitamin K deficient. Newborn babies are given vitamin
K soon after birth to prevent bleeding.
Broad spectrum antibiotics also deplete the normal E Coli
bowel flora.
N ll th bl d i li id i id th bl d l
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Normally the blood remains liquid inside the blood vessels.
There are two systems that initiate blood clotting:
The Intrinsic System and the Extrinsic System.
The Intrinsic pathway can be initiated by events that take
place within the lumen of blood vessels.
The Intrinsic pathway requires only elements (clotting factors,
Ca++, platelet surface etc.) found within, orintrinsic to thevascular system.
The Extrinsic pathway is the other route to coagulation.
It requires Tissue Factor (tissue thromboplastin), a substancewhich is "extrinsic to", or not normally circulating in the
vessel.
Tissue Factor is released when the vessel wall is ruptured.
T t f d t di l th
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Tests performed to diagnose a coagulopathy
Prothrombin Time (PT)
To measure the Extrinsic system
Will be abnormal if there are deficiencies in the following factors:
I, II, V, VII, X
Activated Partial Thrombin Time (APTT)
To measure the Intrinsic system
Will be abnormal if there are deficiencies in the following factors:
I, II, V, VIII, IX, X, XI, XII
Thrombin Time (TT)
Will be abnormal if there are deficiencies in the following factors:
I
Test for Common pathway:
Both A.P.T.T. and P.T.
There is NO single screening test for the Common Pathway
T t f d t di l th t
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Tests performed to diagnose a coagulopathy - cont
D-Dimer:
When the clot breaks down (fibrin degrading) it releases fibrin degradation
products. D-Dimer measures these breakdown products.
Platelet Aggregation test:
The platelet aggregation test aids in the evaluation of bleeding disorders by
measuring the rate and degree to which platelets form a clump (aggregate) after
the addition of a chemical that stimulates clumping (aggregation).Several different substances called agonists are used in the test.
These agonists include adenosine diphosphate, (ADP) epinephrine, thrombin,
collagen, and ristocetin.
An agonist is a chemical that binds to a receptor of a cell and triggers a
response by that cell.
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Old Tests
Bleeding timeTests vascular integrity and platelet function
Incision on volar aspect of the forearm 1mm deep
and 1 cm long
BP cuff inflated to 40 mmHgNormal < 8 minutes
Borderline 8-10 minutes
Abnormal 10 + minutes
Affected by ASA (acetylsalicylic acid, Aspirin ) (permanent)and NSAIDs
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Thromboasthenia
Platelet function disorder
Tests:
Old Tests:
Bleeding & Clotting time
New Test:
PFA 100
Plate Function Analysis 100
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Normal Reference Range:
The Normal Reference Range for a particular test or measurement is usually
defined as the prediction interval between which 95% of values of the healthy
population fall into, whatever the distribution of these values. In case of normal
distribution, it can alternatively be defined as the interval limited by 2 standard
deviations from either side of the mean.
It is sometimes referred as "reference interval", normal range or normal values(and sometimes "usual" range/values). All these terms should be discouraged as
not everyone outside the interval is abnormal, and people who have a particular
condition may still fall within this interval.
Therapeutic range:
The range of concentrations at which a drug or other therapeutic agent is effective
with minimal toxicity to most patients.
A minimum of 100 patients are selected to establish a
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Total = 95.4%
A minimum of 100 patients are selected to establish a
Normal Reference Range
Within 2 Standard Deviations
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