16. Coagulation Flashcards
What is hemostasis?
ability of body’s systems to maintain integrity of blood and blood vessels - defined as stopping of bleeding
involves several complex pathways, platelets, and coagulation factors
Alterations in any of these can cause bleeding disorders
What are the elements of hemostasis?
endothelial cells that line the walls of blood vessels - in health, have anticoagulant properties
Platelets
Coagulation/clotting factors - found in plasma in sm concentrations
What are the two parts of hemostasis?
MECHANICAL: initiated when there is tear/damage to blood vessel wall > exposed subendothelium is a charged surface which attracts platelets > von Willebrand factor req for platelet adhesion, it stabilizes platelet plug > adhesion causes platelets to release factors that initiate chemical phase of blood coagulation
CHEMICAL: coagulation cascade
What is the coagulation cascade?
12 diff factors 1-13, no factor 11
Each step triggers next reaction in pathway
End result is a mesh of crosslinked, insoluble, fibrin strands that form blood clot
What are cascade cofactoes?
entire clotting process reqs many cofactors including Vit K and Ca
Multiple feedback loops - to accelerate process when needed and inhib process when necessary
What are the blood hemostasis mechanisms?
Coagulation cascade is divided into three pathways, the divisions are artificial
intrinsic pathway - intravascular
Extrinsic - within tissue, helps to initiate intrinsic
common - where the two systems meet
absence of a single factor in any of the three will = coag deficiencies
we use these systems to help diagnose and pinpoint the coagulopathy
What is the primary clot formation?
Platelet plug
An injured blood vessel will constrict, if defect is small, blood flow may stop
Damage to vessel wall exposes collagen which triggers platelets to adhere and aggregate to it
Activated platelets: release granules that recruit other platelets to sit, triggers coagulation cascade and forms the primary clot
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 is secondary clot fromation
process of stablizing primary clot or platelet plug
Fibrin adheres to the platelets and holds them together like a net
The adherence of fibrin strands is result of numerous coagulation factors
both primary and secondary clot formation occurs simultaneously
What is degradation of blood clot?
as important as it is for blood clots to form when vascular damage occurs, important that body has mechanism in which to break down blood clots, and inhib unnecessary clot formation - a series of reactions perform these functions
Tissue plasminogen activator (tPA) and plasmin: break down soluble fibrin into fibrin degradation products (FDPs)
break down insoluble fibrin into cross-linked FDP’s and D-dimers
What do we need to keep aware of when collecting and handling samples?
Collect quickly w/ little tissue damage as possible
Reduce patient excitement bc w/ inc platelet count and activation, von Willebrand factor, Factors 1, 5 and 13
What catheter do we never collect a sample from? Instead, what should we use?
An indwelling cath bc sm amounts of fibrin, fibrinogen and platelets usually present within cath
If poss, use vacutainer to help relim or reduce platelet activate
What is the preferred anticoagulant for clotting tests?
sodium citrate - much remember 10% dilution factor and correctly our count
What is the preferred tube when doing platelet counts?
EDTA
What tube might we use for blood transfusions?
sodium citrate
Do we use anticoagulant when doing whole blood counting time and activated coagulation?
No
What is the proper fill ratio of sodium citrate and whole blood
1NaCitrate:9whole blood
Do anemic patients have shortened or increased clotting times. WHy?
Shortened clotting times bc increased plasma V compared to a non-anemic patient, therefore, sample will be under-citrated
WIll a polycythemic and dehydrated patient have prolonged, normal or increased clotting times?
decreased plasma V compared to a normal patient, therefore, over-citrated
When we are about to run a test, how long do we have? How do we handle our tube?
<2hrs of collection
Keep tube upright, tightly sealed and at room temp
Avoid vibrations
What are the requirements for shipping?
centrifuge for 15m
withdraw plasma w/o disturbing platelet layer
put in a plastic tube and freeze
ship on dry ice
What is coagulation instrumentation?
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
What is a fibrometer?
semi-automated machine - coagulation study, citrated sample
What is thromboelastography?
performed by several analuyzers
some use fresh whole blood, others citrated
analyze entire clotting process from formation of initial clot to fibrinolysis
results in graph format = time for clot formation to occur, strength of clot, time for clot breakdown
Describe whether the patient is hypercoagulable vs hypo
What are platelet function analyzers?
evals platelet adhesion and aggregation
uses cartridges that contain a collagen coated membrane
Platelets adhere to membrane and 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 vet med
What are point of care analyzers?
hand held instruments
I-stat machine validated for vet med
What is the coag Dx analyzer?
can use fresh whole blood or citrated-anticoag blood
uses cartridges that contain reagents
Available tests
prothrombin time (PT) for fel, k9 and eq. Activated partial thromboplastin time (PTT) - feel and k9
What is coagulation testing?
diff tests eval specific phases of the coag process - automated tests preferred over manual tests
important that a consistent approach is used when eval patients
a CBC should always be performed along w/ coagulation testing - a platelet count should always be performed - thrombocytopenia can invalidate some test results
What is buccal mucosa bleeding time?
used to detect abnormalities in platelet func
common signs include petechia, epistaxis and hematuria
Test procedure: sedate/anes anim in lat recumbency, upper lip folded up and secured in place, a spring-loaded lancet is placed against the mucosal surface @ premolar area
Lancet trigger is depressed w/o pressing the device against mucosa, start timer, 1mm deep incision made
Every 5s wick blood away w/ filter paper w/o touching incision
endpoint is reached when blood no longer appears at sight (paper no longer soaks up free flowing blood
time recorded
Do we normally test 1 or more spots with BMBT?
yes, often 2 sites tested and mean time btw patient is taken as patient’s value
Normal values btw 1-5m
prolonged times seen w/ platelet dysfunction, von willebrand factor deficiencies, or thrombocytopenia
What is activated clotting time?
tests all major clotting factors exceppt 12
can be performed by manual methods or automated
will be prolonged if patient is severely thrombocytopenia
prolonged abnormalities in intrinsic pathway
What is whole blood clotting time?
tests the intrinsic system
not commonly performed as ACT tests more sensitive - manual test
normal values
Bovine: 4-15m
K9: 6-8m
Eq: 4-15m
What is the activated partial thromboplastin time? PTT or aPTT
this is a test of the intrinsic and common clotting mechanisms
Citrated plasma is used - incubated w/ a factor 12 activator, a platelet substitute and calcium. Time is measured from calcium addition to the sample and fibrin formations
Timing is crucial and controls should always be run w/ tests
Prolonged times occur w/ heparin administration, many hereditary and acquired coagulation disorders
What is prothrombin time?
AKA one-stage prothrombin time tests (OSPT)
method tests extrinsic and common pathways
tissue thromboplastin reagent is added to citrated plasma
system is activated w/ addition of calcium
controls should be used
Coag Dx will have ability to run both PTT and PT tests
What might cause prolonged prothrombin times?
dietary deficiency of Vit K
Vit K antagonist rodenticide toxicity
dicoumarol (spoiled sweet clover) toxicity
severe liver disease(coagulation factors are prod in the liver)
A hereditary and acquired deficiency of any of the factors in the extrinsic cascade
DIC
What is the clot retraction test?
evals intrinsic and extrinsic pathways as well as platelet number and func
Test results only indicate that there is a coagulopathy, not which pathway is involved
manual test that takes 24hr to complete
What is fibrinogen determination?
automated analyzers generally use electrochemical methods
manual test method as well
What is PIVKA?
Proteins that are Induced by the absence of Vitamin K
Vitamin K req to activate several of the clotting factors - 2, 6, 9, and 10
when vitamin K is not present, the precursors to these coagulation factors will build up in the blood - proteins are detected by PIVKA testing or by thrombotest
What does the PIVKA test help to differentiate?
rodenticied toxicity and primary hemophilia in patients where ACT is prolonged
considered more sensitive than PTT or PT tests for rodenticide toxicity - lvls can be elevated as soon as 6 hrs post ingestion of rodenticides
What is D-dimer and fibrin degredation products?
evals tertiary hemostasis - breakdown of clots or fibrinolysis
D-dimers and fibrin degradation products (FDPs) are prod when a clot breaks down
Used to diagnose DIC, provide dx info in patients w/ liver failure, trauma and hermangiosarcoma
In house k( D-dimer test available
D-dimer tests more specific and sensitive for determining fibrinolysis
What is von Willebrand factor
required for platelet adhesion
testing is req when platelet func defects are detected, done at ref labs
