Coagulation Flashcards
Homeostasis means
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
The primary elements of hemostasis is
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
What are the two parts to the coagualtion process
Chemical and mechanical
What is the mechanical process of caogulation
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
What is the chemical process for coagulation
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
What is the coagulation cascade
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
What are cascade cofactors for coagualtion
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
What are the three sections of the coagulation cascade
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
Blood hemostasis is useful for
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
Primary clot factor is and for what
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
What do activated platelets do
Release granules that recruit other platelets to the site
Triggers the coagulation cascade and forms the primary clot
What is secondary clot formation and how does it happen
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
How does a blood clot degrade
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
Why is the degradation of the blood clot important
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
How to collect the sample for coagualtion tests
When collecting samples for coagulation testing, the sample must be collected quickly and with as little tissue damage as possible
What should you do with a patient that you need a sample from for coagulation tests
Reduce patient excitement as it can cause artificial increases of:
Platelet counts and activation of platelets
Von Willebrand factor
Factors I, V and VIII
What tools should you use to collect blood for a coagulation test
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
When would you use each coloured blood tube
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
What is the appropriate amount of sodium to whole blood
Proper fill ratio is one part sodium citrate to nine parts whole blood
Ratio is based on plasma volume
What is unique with clotting time and anemic patients
Anemic patients will have shortened clotting times
Increased plasma volume compared to a non-anemic patient, therefore sample will be “under-citrated”
What is unique in clotting time for dehydrated patients
Polycythemic and dehydrated patients will have prolonged clotting times
Decreased plasma volume compared to a normal patient, therefore sample will be “over-citrated”
What to do after a sample is collected for a coagulation test
The tests should be run within 2 hours of sample collection
Keep the tube upright, tightly sealed and at room temperature
Avoid vibrations
What should you do for a coagulation sample that needs shipping
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
What is commonly used to perform a coagulation test
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
Fibrometer is and used for
Not common anymore
Semi-automated machine–can perform a number of coagulation studies
Citrated sample
Thromboelastography is and used for
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
Thromboelastography has what results
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
Platelet function analyzer is and used for
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
Point of care analyzers are
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
Coag Dx analyzer is
Can use fresh whole blood or citrated- anticoagualted blood
Uses cartridges that contain reagents
What are the tests available under the coag dx
Prothrombin time (PT)
For feline, canine and equine patients
Activated partial thromboplastin time (PTT)
For feline and canine patients
Coagulation testing is and used for
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
Buccal mucosa bleeding time is
Used to detect abnormalities in platelet function
Common clinical signs include petechiae, epistaxis and hematuria
What is the test procedure with a buccal mucosal bleeding time
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
Activated clotting time is
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
Whole blood clotting time
This test the intrinsic system
Not commonly performed anymore as the ACT test are more sensitive
Manual test
Normal whole blood clotting times
Bovine: 4 – 15 minutes
Canine: 6 – 8 minutes
Equine: 4 – 15 minutes
Activated partial thromboplastin time (PTT) or (aPTT) is
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
Activated partial thromboplastin time (PTT) or (aPTT) what sample do you use and why
Incubated with a factor XII activator, a platelet substitute and calcium
Time is measured from calcium addition to the sample and fibrin formation
Prothrombin time is
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
Why can you have a prolonged prothrombin time
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
Clot reaction test is
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
Fibrinogen determination is
Automated analyzers generally use electrochemical methods
Manual test method as well
PIVKA is and measures
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
D-dimer and fibrin degradation products is
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
What are the D-dimer and fibrin degradation test used for
These tests are used to:
Diagnose DIC
Provide diagnostic information in patients with liver failure, trauma, and hemangiosarcoma
von Willebrand factor is
Required for platelet adhesion
Testing is requested when platelet function defects are detected
Testing is done at reference labs