16. Coagulation

Question 1

What is hemostasis?

Answer 1

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

Question 2

What are the elements of hemostasis?

Answer 2

endothelial cells that line the walls of blood vessels - in health, have anticoagulant properties
Platelets
Coagulation/clotting factors - found in plasma in sm concentrations

Question 3

What are the two parts of hemostasis?

Answer 3

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

Question 4

What is the coagulation cascade?

Answer 4

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

Question 5

What are cascade cofactoes?

Answer 5

entire clotting process reqs many cofactors including Vit K and Ca
Multiple feedback loops - to accelerate process when needed and inhib process when necessary

Question 6

What are the blood hemostasis mechanisms?

Answer 6

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

Question 7

What is the primary clot formation?

Answer 7

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

Question 8

What is secondary clot fromation

Answer 8

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

Question 9

What is degradation of blood clot?

Answer 9

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

Question 10

What do we need to keep aware of when collecting and handling samples?

Answer 10

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

Question 11

What catheter do we never collect a sample from? Instead, what should we use?

Answer 11

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

Question 12

What is the preferred anticoagulant for clotting tests?

Answer 12

sodium citrate - much remember 10% dilution factor and correctly our count

Question 13

What is the preferred tube when doing platelet counts?

Answer 13

EDTA

Question 14

What tube might we use for blood transfusions?

Answer 14

sodium citrate

Question 15

Do we use anticoagulant when doing whole blood counting time and activated coagulation?

Answer 15

No

Question 16

What is the proper fill ratio of sodium citrate and whole blood

Answer 16

1NaCitrate:9whole blood

Question 17

Do anemic patients have shortened or increased clotting times. WHy?

Answer 17

Shortened clotting times bc increased plasma V compared to a non-anemic patient, therefore, sample will be under-citrated

Question 18

WIll a polycythemic and dehydrated patient have prolonged, normal or increased clotting times?

Answer 18

decreased plasma V compared to a normal patient, therefore, over-citrated

Question 19

When we are about to run a test, how long do we have? How do we handle our tube?

Answer 19

<2hrs of collection
Keep tube upright, tightly sealed and at room temp
Avoid vibrations

Question 20

What are the requirements for shipping?

Answer 20

centrifuge for 15m
withdraw plasma w/o disturbing platelet layer
put in a plastic tube and freeze
ship on dry ice

Question 21

What is coagulation instrumentation?

Answer 21

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 22

What is a fibrometer?

Answer 22

semi-automated machine - coagulation study, citrated sample

Question 23

What is thromboelastography?

Answer 23

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

Question 24

What are platelet function analyzers?

Answer 24

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

Question 25

What are point of care analyzers?

Answer 25

hand held instruments I-stat machine validated for vet med

Question 26

What is the coag Dx analyzer?

Answer 26

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

Question 27

What is coagulation testing?

Answer 27

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

Question 28

What is buccal mucosa bleeding time?

Answer 28

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

Question 29

Do we normally test 1 or more spots with BMBT?

Answer 29

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

Question 30

What is activated clotting time?

Answer 30

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

Question 31

What is whole blood clotting time?

Answer 31

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

Question 32

What is the activated partial thromboplastin time? PTT or aPTT

Answer 32

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

Question 33

What is prothrombin time?

Answer 33

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

Question 34

What might cause prolonged prothrombin times?

Answer 34

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

Question 35

What is the clot retraction test?

Answer 35

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

Question 36

What is fibrinogen determination?

Answer 36

automated analyzers generally use electrochemical methods manual test method as well

Question 37

What is PIVKA?

Answer 37

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

Question 38

What does the PIVKA test help to differentiate?

Answer 38

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

Question 39

What is D-dimer and fibrin degredation products?

Answer 39

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

Question 40

What is von Willebrand factor

Answer 40

required for platelet adhesion testing is req when platelet func defects are detected, done at ref labs