Coagulation

Question 1

Homeostasis means

Answer 1

Hemostasis is the ability of the body’s systems to maintain the integrity of the blood and blood vessels
In other words, it is defined as the stopping of bleeding (aka– blood coagulation)
It involves several complex pathways, platelets, and coagulation factors
Alterations in any of these can cause a bleeding disorder

Question 2

The primary elements of hemostasis is

Answer 2

Endothelial cells that line the walls of blood vessels
In health, they have anticoagulant properties
Platelets
Coagulation/clotting factors
They are found in the plasma in small concentrations

Question 3

What are the two parts to the coagualtion process

Answer 3

Chemical and mechanical

Question 4

What is the mechanical process of caogulation

Answer 4

Initiated when there is a tear or damage to a blood vessel wall
The exposed subendothelium is a charged surface which attracts platelets
von Willebrand factor is required for platelet adhesion, it stabilizes the platelet plug
The adhesion causes platelets to release factors that initiate the chemical phase of blood coagulation

Question 5

What is the chemical process for coagulation

Answer 5

The chemical phase is known as the coagulation cascade
Remember that the pathways of coagulation are interrelated, interdependent and at least partially cell-based
Each step of the coagulation cascade is dependent on the activation of the clotting factors in the previous steps

Question 6

What is the coagulation cascade

Answer 6

There are 12 different coagulation factors (Factors I to XIII, there is no Factor XI)
Table 14-1 page 87
Each step triggers the next reaction in the pathway
The end result is a mesh of cross linked, insoluble, fibrin strands that form the blood clot
The final phase of hemostasis is the degradation of the fibrin clot

Question 7

What are cascade cofactors for coagualtion

Answer 7

The entire clotting process requires many cofactors including Vitamin K and calcium
There are multiple feedback loops
These loops accelerate the process when needed and inhibit the process when necessary

Question 8

What are the three sections of the coagulation cascade

Answer 8

The coagulation cascade is divided into three pathways, although the sections work together – the divisions are artificial
Intrinsic pathway – intravascular
Extrinsic pathway – within the tissue, helps to initiate the intrinsic pathway
Common pathway – is where the two systems meet

Question 9

Blood hemostasis is useful for

Answer 9

The coagulation cascade is divided into three pathways, although the sections work together – the divisions are artificial
The absence of a single factor in any of the three sections will result in coagulation deficiencies
We use these systems to help diagnose and pinpoint the coagulopathy

Question 10

Primary clot factor is and for what

Answer 10

An injured blood vessel will constrict almost immediately
If the defect is small enough, blood flow is stopped
Damage to the vessel wall exposes collagen which triggers platelets to adhere to and aggregate to it
The platelet-collagen complex releases several chemical messengers (coagulation factors) as well as provides a cellular matrix for the main clot to adhere to

Question 11

What do activated platelets do

Answer 11

Release granules that recruit other platelets to the site
Triggers the coagulation cascade and forms the primary clot

Question 12

What is secondary clot formation and how does it happen

Answer 12

This is the process of stabilizing the primary clot or platelet plug
Fibrin adheres to the platelets and holds them together like a net
The adherence of fibrin strands is the result of numerous coagulation factors
Both primary and secondary clot formation occur simultaneously

Question 13

How does a blood clot degrade

Answer 13

Tissue plasminogen activator (tPA) and plasmin:
Break down soluble fibrin into fibrin degradation products (FDPs)
Break down insoluble fibrin into cross-linked FDPs and D-dimers

Question 14

Why is the degradation of the blood clot important

Answer 14

As important as it is for blood clots to form when vascular damage occurs, it is also important that the body has a mechanism in which to break down blood clots, and inhibit unnecessary clot formation
A series of reactions perform these functions

Question 15

How to collect the sample for coagualtion tests

Answer 15

When collecting samples for coagulation testing, the sample must be collected quickly and with as little tissue damage as possible

Question 16

What should you do with a patient that you need a sample from for coagulation tests

Answer 16

Reduce patient excitement as it can cause artificial increases of:
Platelet counts and activation of platelets
Von Willebrand factor
Factors I, V and VIII

Question 17

What tools should you use to collect blood for a coagulation test

Answer 17

Never collect samples for testing for coagulopathies from an indwelling catheter
Small amounts of fibrin, fibrinogen and platelets are usually present within catheters
If possible, use a vacutainer when collecting the sample
Helps eliminate or reduce platelet activation
Preferred anticoagulant is sodium citrate
When doing platelet counts with this sample you must remember the 10% dilution factor and correct your count

Question 18

When would you use each coloured blood tube

Answer 18

For platelet counts EDTA it the preferred anticoagulant
Sodium citrate anticoagulant is also used for blood transfusions
When performing whole blood clotting time and activated coagulation time, no anticoagulant is used
When required, sodium citrate tubes are the first anticoagulant tubes to be filled

Question 19

What is the appropriate amount of sodium to whole blood

Answer 19

Proper fill ratio is one part sodium citrate to nine parts whole blood
Ratio is based on plasma volume

Question 20

What is unique with clotting time and anemic patients

Answer 20

Anemic patients will have shortened clotting times
Increased plasma volume compared to a non-anemic patient, therefore sample will be “under-citrated”

Question 21

What is unique in clotting time for dehydrated patients

Answer 21

Polycythemic and dehydrated patients will have prolonged clotting times
Decreased plasma volume compared to a normal patient, therefore sample will be “over-citrated”

Question 22

What to do after a sample is collected for a coagulation test

Answer 22

The tests should be run within 2 hours of sample collection
Keep the tube upright, tightly sealed and at room temperature
Avoid vibrations

Question 23

What should you do for a coagulation sample that needs shipping

Answer 23

Centrifuge at 2500 g for 15 minutes (or whole blood setting)
Withdraw plasma without disturbing the platelet layer
Put in a plastic tube and freeze
Ship on dry ice

Question 24

What is commonly used to perform a coagulation test

Answer 24

Automated machines are preferred over manual methods
They test for specific parts of the coagulation process
Platelet function
Some analyze multiple chemical components
Liquid reagents are used to reverse the action of the anticoagulant
The analyzer then monitors the sample for clot formation

Question 25

Fibrometer is and used for

Answer 25

Not common anymore
Semi-automated machine–can perform a number of coagulation studies
Citrated sample

Question 26

Thromboelastography is and used for

Answer 26

Performed by several analyzers
Some use fresh whole blood others use citrated samples
Analyze the entire clotting process from formation of initial clot to fibrinolysis

Question 27

Thromboelastography has what results

Answer 27

Results are generally in a graph format
Time for clot formation to occur
Strength of clot
Time for clot breakdown
Describe whether the patient is hypercoagulable or hypocoagulable
Usefulness of these methods within veterinary medicine is questionable

Question 28

Platelet function analyzer is and used for

Answer 28

Evaluates platelet adhesion and aggregation
Uses cartridges that contain a collagen coated membrane
The platelets adhere to the membrane and the time is recorded until blood flow is no longer occurring
The PFA-100 analyzer has been validated for use in dogs
Most machines are not validated for use in veterinary medicine

Question 29

Point of care analyzers are

Answer 29

Hand held instruments
Most are used in human field and not validated for veterinary use
Includes i-Stat machine which is validated for animal use

Question 30

Coag Dx analyzer is

Answer 30

Can use fresh whole blood or citrated- anticoagualted blood
Uses cartridges that contain reagents

Question 31

What are the tests available under the coag dx

Answer 31

Prothrombin time (PT)
For feline, canine and equine patients
Activated partial thromboplastin time (PTT)
For feline and canine patients

Question 32

Coagulation testing is and used for

Answer 32

Different tests evaluate specific phases of the coagulation process
Automated tests are preferred over manual tests
It is important that a consistent approach is used when evaluating patients
A CBC should always be performed along with coagulation testing
Most importantly, a platelet count should always be performed
Thrombocytopenia can invalidate some test results

Question 33

Buccal mucosa bleeding time is

Answer 33

Used to detect abnormalities in platelet function
Common clinical signs include petechiae, epistaxis and hematuria

Question 34

What is the test procedure with a buccal mucosal bleeding time

Answer 34

The animal is sedated or anaesthetised and put in lateral recumbency
The upper lip is folded up an secured in place
A spring loaded lancet is placed against the mucosal surface at the premolar area
The lancet trigger is depressed without pressing the device against the mucosa, simultaneously strat timer
1 mm deep incision is made
Every 5 seconds wick the blood way with filter paper without touching the incision
The endpoint is reached when blood no longer appears at the site (the paper no longer soaks up free flowing blood)
Often two sites are tested and the mean time between them taken as the patients value
Normal values are between 1-5 minutes
Prolonged times are seen with platelet dysfunction, von Willebrand factor deficiencies or thrombocytopenia

Question 35

Activated clotting time is

Answer 35

Test all major clotting factors except factor VII
Can be performed by manual methods
Automated analyzers are the preferred method for testing
i-STAT
Will be prolonged if the patient is severely thrombocytopenic
Prolonged with abnormalities in the intrinsic pathway

Question 36

Whole blood clotting time

Answer 36

This test the intrinsic system
Not commonly performed anymore as the ACT test are more sensitive
Manual test

Question 37

Normal whole blood clotting times

Answer 37

Bovine: 4 – 15 minutes
Canine: 6 – 8 minutes
Equine: 4 – 15 minutes

Question 38

Activated partial thromboplastin time (PTT) or (aPTT) is

Answer 38

This is a test of the intrinsic and common clotting mechanisms
Citrated plasma is used
Timing is crucial and controls should ALWAYS be run with the tests
Prolonged times occur with heparin administration, and many hereditary and acquired coagulation disorders

Question 39

Activated partial thromboplastin time (PTT) or (aPTT) what sample do you use and why

Answer 39

Incubated with a factor XII activator, a platelet substitute and calcium
Time is measured from calcium addition to the sample and fibrin formation

Question 40

Prothrombin time is

Answer 40

Also known as one-stage prothrombin time tests (OSPT)
This method tests the extrinsic and common pathways
Tissue thromboplastin reagent is added to citrated plasma
The system is activated with the addition of calcium
Controls should be used
Coag Dx™ will has the ability to run both PTT and PT tests

Question 41

Why can you have a prolonged prothrombin time

Answer 41

A dietary deficiency of vitamin K
Vitamin K antagonist rodenticide toxicity
Dicoumarol (spoiled sweet clover) toxicity
Severe liver disease
A hereditary or acquired deficiency of any of the factors in the extrinsic cascade
DIC

Question 42

Clot reaction test is

Answer 42

Evaluates the intrinsic and extrinsic pathways as well as platelet number and function
Test results only indicate that there is a coagulopathy, not which pathway is involved
Manual test that takes 24 hours to complete

Question 43

Fibrinogen determination is

Answer 43

Automated analyzers generally use electrochemical methods
Manual test method as well

Question 44

PIVKA is and measures

Answer 44

Refers to the Proteins that are Induced by the absence of Vitamin K
Vitamin K is required to activate several of the clotting factors
II, VII, IX, and X
When vitamin K is not present, the precursors to these coagulation factors will build up in the blood
The proteins are detected by PIVKA testing or by the Thrombotest
This test helps to differentiate between rodenticide toxicity and primary hemophilia in patients where ACT is prolonged
Considered more sensitive than PTT or PT tests for rodenticide toxicity
Levels can be elevated as soon as 6 hours post ingestion of rodenticides
BUT lots of controversy on whether it is actually useful

Question 45

D-dimer and fibrin degradation products is

Answer 45

Both tests are used to evaluate tertiary hemostasis
The breakdown of clots or fibrinolysis
D-dimers and fibrin degradation products (FDPs) are produced when a clot breaks down
An in-house canine D-dimer test is available
D-Dimer tests are more specific and sensitive for determining fibrinolysis

Question 46

What are the D-dimer and fibrin degradation test used for

Answer 46

These tests are used to:
Diagnose DIC
Provide diagnostic information in patients with liver failure, trauma, and hemangiosarcoma

Question 47

von Willebrand factor is

Answer 47

Required for platelet adhesion
Testing is requested when platelet function defects are detected
Testing is done at reference labs