LAB - Hemostasis Flashcards
Prothrombin time
measures the time to form a clot when calcium and tissue thromboplastin (FIII or TF) are added to citrated plasma
what does Warfarin do t the vitamin K-dependent clottingfactors?
- II, VII, IX, X
- prevents y-carboxylation of terminal AAs which is required for binding to calcium and interaction with platelet phospholipid
rate of clotting in PT dependent on
the nature of tissue thromboplastin used (human brain more sensitive to levels of coag than is rabbit brain thromboplastin)
purpose of the international sensitivity index
allows each lab to express results as they would be had the international primary std thromboplastin of ISI = 1.0 been used
reagents used in PT
- tissue thromboplastin = reconstitute; 15 mins
- control: commercial lyophilized citrated plasma; reconstitute; 15 minutes
- test plasma: from 3.2% sodium citrate; centrifuge at 2500 g for 10 mins; if not in use within 24 hrs, remove to plastic tubes and store at -20C for no longer than 2 weeks
KC1 analyzer
- metal ball in testing cup attracted to a magnet within the instrument
- cup rotates = ball remains attracted to magnet = stays in place if no clot
- as thromboplastin is added to plasma = clot = contents of cup becomes more viscous = ball no longer attracted to magnet
- timer stops
STart-4
- metal ball in the cuvette oscillates between two magnets
- clot forms = viscosity increases = ball stops moving
causes of prolonged prothrombin times
- factor def = II, V, VII, X, or fibrinogen
- coag factor inhibitors
- oral anticoag therapyu
- vit k deficiency
- DIC
- liver damage
causes of shortened PT
- multiple myeloma
- myocardia infarction
- drug therapy
PTT reagent contains a activator such as
MICRONIZED SILICA
- ALSO CONTAINS PHOSPHOLIPID (PF3)
aPTT = contact factors of intrinsic clotting cascade activated by the silica to the level of…
XIa
- subsequent addition of calcium chloride allow progression to a fibrin clot
causes of prolonged PTT times
- deficiency of factors HMWK, PK, XII, XI, IX, VIII, X, V, prothrombin, fibrinogen
may be related to:
- inherited factor def
- anticoag therapy w/ heparin or warfarin
- secondary fibrinolysis (DIC consuming factors)
- liver disease = impaired synthesis
- vitamin K deficiency
Or
- pathological inhibitors (including lupus anticoagulant)
some reasons why PTT reference range could change
- different Lot #’s = preparations of reagents vary
- automated vs manual methods
- test population = depends
- means of detecting endpoint
In a mixing stud, correction of the clotting time cannot rule out a what…
delayed- reacting inhibitor
- results will provide direction on the next steps of testing to determine cause of prolonged PT or PTT
fibrinogen assay
dilutions of fibrinogen standard of known concentration and patient plasma are clotted ith n EXCESS amount of thrombin
reagents in a fibrinogen assay
- standard
- thrombin
- control plasma
- *reconstitute according to instructions**
- test plasma
- Owren’s Veronal buffer (pH 7.35)
T or F. Samples with high fibrinogen concentrations will have short clotting times
T
- further dilute such plasmas (120 total), repeat test and multiply graph reading by 2
- very low fibrinogen concentrations require less dilution
how can thrombin be prevented from acting on fibrinogen
by heparin
- in anticoag patients
OR
by early fibrinogen and fibrin split products (patents with fibrinolysis); fibrinogen assay avoids these potential interferences through the use of excess thrombin
testing for FVIII deficiency is based on …
the PTT method
how does a FVIII specific assay work?
- ability of dilutions of patient plasma to correct the prolonged PTT of factor VIII deficient (substrate) plasma is measured
- clotting time compared to those obtained when dilutions of normal plasma of known factor conctn (Std plasma) are similarly added to FVIII deficient plasma
decrased FVIII
- hemophilia
- vWD
- DIC
- liver disease
increased FVIII
- inflammation with increased acute phase reactant
- immediately following surgery
primary fibrinolysis
- high levels of plasmin
- unopposed by antiplasmins
- circulating fibrinogen cleaved by plasmin = FDPs
secondary fibrinolysis
- inappropriate activity of the fibrinolytic system
- increased activity due to the formation of intravascular clots
- fibrin clots will be the target of plasmin = FDPs and D-dimer fragments
secondary fibrinolysis
- inappropriate activity of the fibrinolytic system
- increased activity due to the formation of intravascular clots
- fibrin clots will be the target of plasmin = FDPs and D-dimer fragments
this test is helpful in distinguishing between primary and secondary fibrinolysis
D-dimer test
thrombolytic therapy required by patients with…
potentially life-threatening clots such as DVT, PE, and blocked coronary arteries
difference between anticoagulant therapy and thrombolytic therapy
- anticoags = prevent inappropriate clotting
- thrombolytic therapy = dissolve existing clots
> streptokinase, urokinase, rTPA
> promote generation of plasmin for clot lysis = thrombin time to monitor
why is thrombin time useful for monitoring thrombolytic therapy
- reflects fibrinogen levels
> risk of therapy is that plasmin generated will indiscriminately lyse both fibrin and fibrinogen; hemorrhage if fibrin is depleted - thrombin time responds to presence of FDPs, which are indicators that thrombolysis is taking place
compared to thrombin time, this is a more specific indicator of clot lysis
D-Dimer test
- recognizes fragments form cross-linked fibrin degradation
D-Dimer Test
latex particles coated with monoclonal antibody to D-Dimer (mouse anti-human D-dimer) will specifically detect D-dimers in test plasma
test sample for D-Dimer test
fresh, citrated, EDTA or heparinized plasma
Notes for D-Dimer Test
- do not allow mixtures to dry
- read at exactly three minutes
- serum can be used but plasma is preferred as D-Dimers may get trapped within the clot
- false positive can occur in presence of rheumatoid factor
increased levels of D-Dimers are seen in:
- DVT
- PE
- DIC
- hemorrhage
- surgical patients
- cancers and cirrhosis
what is thrombin time?
measures the time taken to form a fibrin clot when thrombin acts on fibrinogen in a plasma sample
- fibrin formation is triggered when thrombin is added to the patient plasma (bypasses prior steps in cascade)
- thrombin time affected by low fibrinogen (hypo-), dysfunctional fibrinogen (dys-), and the presence of circulating anticoags (heparin and FDPs)
a prolonged TT may be due to
- decreased levels of fibrinogen (acquired or inherited)
- abnormally functioning fibrinogen
- thrombin inhibitors (FDPs, heparin)
FXIII
converts hydrogen bonds b/w fibrin monomers to covalent bonds
FXIII screening test
- if absent, clots are soluble in 1% monochloroacetic acid = should take more than 1 hr for clot to dissolve OR 5M urea (more than 24 hrs)
abnormal clot solubility (disappearance of clots) seen in
- inherited lack of FXIII (or abnormal)
- DIC
- liver disease
what are potential complications for DVT?
- amputation
- chronic illness => post-thrombotic sybdrome
- could dislodge and travel to lungs = PE (fatal if large and blocks blood flow to lungs)
in those at risk for DVT, how can it be prevented?
- compression socks
- healthy diet
- no smoking
- anticoags therapy
- adequate hydration for fluid blood
- exercise
two substances responsible for a prolonged thrombin time, but do not affect fibrinogen
- heparin
- FDP
- *thrombin in excess in fibrinogen assay**
