Coagulation Flashcards
Thromboelastography / Thromboelastometry - What is tested?
- Tests global coagulation
- From initial clot formation through to fibrinolysis
What are the measured variables with TEG/TEM?
What do each of the variables relate to in vivo?
- R value (reaction time)
- Time until first evidence of clot formation
- This provides an indication of clotting time
- K
- Time from clot initiation (end of R) to clot reaching 20 mm
- Measures the speed of clot formation and is a reflection of polymerization or clot kinetics
- Angle
- measures the tangent of clot length over time - similar information to K
- MA
- Maximal ampiltude
- Provides an indication of overall clot strength
- Fibrinolysis
- EPL - estimated percent lysis
- % lysis after 30 minutes
TEM / ROTEM - Pros and Cons
Pros:
- Includes cells in evaluation of clotting
Cons:
- Poor reproducibility without a strong tissue factor
- Results altered by platelet number and red cell mass
- Increased time to clot formation with increased HCT
- Longer handling times with lead to activation of the contact pathway, leading to erroneous results
Thrombin-antithrombin complexes - what is tested
A marker of in vivo thrombin activity * Thrombin half life in vivo is extremely short. Stable TAT complexes is an indirect indicator of thrombin generation
Thrombin-antithrombin complexes - Pros and Cons
Pros: * Uses plasma, thus eliminates effect of variable HCT and platelet number Cons: * Expensive and not readily available * Multi-well plate design necessitates batch processing
D- dimers - What is tested?
Degradation of insoluble cross-linked fibrin Increased D dimers indicate: * thrombin generation - fibrin generation, cross linking of fibrin via factor XIII(a) and plasmin activity (to degrade cross linked fibrin.
D-Dimers - Pros and Cons
Pro: * Specific for breakdown of cross-linked fibrin - ie. fibrinolysis * Short half-life (5 hours) means results consistent with recent fibrinolysis. Cons: * Not available widely * Some human assays do not cross react with animal D-Dimers
Fibrinogen degradation products (FDPs) - what is tested?
Specifically tests plasmin activity Breakdown products of fibrinogen, insoluble fibrin, soluble fibrin monomers and cross-linked fibrin
Fibrin degradation products - Pros and Cons
Pros: * Inexpensive and simple to run * In-house testing available Cons: * Not specific for breakdown of cross-linked fibrin * Non specific - can be increased with large number of disorders
Callibrated automated thrombography - What is it?
Evaluates thrombin generation in vitro in response to specific stimuli. The test is run on PRP or PPP but not whole blood
Calibrated automated thrombography - Pros and Cons
Pros: * sensitive evaluation of enzyme contribution to clot formation * can assess platelet contribution with PRP Cons: * Not widely available * Mainly used for research at this time
What tests are available to assess platelets and their function?
- Platelet count - automated and manual 2. Platelet function testing - impedence whole blood platelet aggregometry (Multiplate) * Platelet function analyser (PFA-100)
Describe the function of the PFA-100
PFA-100 measures cessation of while blood flow through an aperture under high shear conditions. * Measures closing time * Membrane coated with collagen and adrenalin or ADP. * Uses sodium citrated blood held at room temperature * Platelet aggregation is dependent on platelet number,, platelet function and functional vWF.
PFA-100: Pros and Cons
Pros: * Simple to use * Accurate and reproducible results * Screening test to exclude severe platelet dysfunction or vWD Cons: * Non-specific for underlying disease process * Will not exclude milder forms of disease
Prothrombin Time (PT) - What is tested
PT evaluates the tissue factor pathway (extrinsic) and common pathway. PT assesses FVII (extrinsic pathway) * citrated plasma is added to CaCl2 and tissue factor in a lipid membrane. PT is the time to first fibrin strands Prolonged PT (normal APTT) indicated FVII deficiency