LAB - Hemostasis

Question 1

Prothrombin time

Answer 1

measures the time to form a clot when calcium and tissue thromboplastin (FIII or TF) are added to citrated plasma

Question 2

what does Warfarin do t the vitamin K-dependent clottingfactors?

Answer 2

• II, VII, IX, X
• prevents y-carboxylation of terminal AAs which is required for binding to calcium and interaction with platelet phospholipid

Question 3

rate of clotting in PT dependent on

Answer 3

the nature of tissue thromboplastin used (human brain more sensitive to levels of coag than is rabbit brain thromboplastin)

Question 4

purpose of the international sensitivity index

Answer 4

allows each lab to express results as they would be had the international primary std thromboplastin of ISI = 1.0 been used

Question 5

reagents used in PT

Answer 5

• 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

Question 6

KC1 analyzer

Answer 6

• 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

Question 7

STart-4

Answer 7

• metal ball in the cuvette oscillates between two magnets

- clot forms = viscosity increases = ball stops moving

Question 8

causes of prolonged prothrombin times

Answer 8

• factor def = II, V, VII, X, or fibrinogen
• coag factor inhibitors
• oral anticoag therapyu
• vit k deficiency
• DIC
• liver damage

Question 9

causes of shortened PT

Answer 9

• multiple myeloma
• myocardia infarction
• drug therapy

Question 10

PTT reagent contains a activator such as

Answer 10

MICRONIZED SILICA

- ALSO CONTAINS PHOSPHOLIPID (PF3)

Question 11

aPTT = contact factors of intrinsic clotting cascade activated by the silica to the level of…

Answer 11

XIa

- subsequent addition of calcium chloride allow progression to a fibrin clot

Question 12

causes of prolonged PTT times

Answer 12

• 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)

Question 13

some reasons why PTT reference range could change

Answer 13

• different Lot #’s = preparations of reagents vary
• automated vs manual methods
• test population = depends
• means of detecting endpoint

Question 14

In a mixing stud, correction of the clotting time cannot rule out a what…

Answer 14

delayed- reacting inhibitor

- results will provide direction on the next steps of testing to determine cause of prolonged PT or PTT

Question 15

fibrinogen assay

Answer 15

dilutions of fibrinogen standard of known concentration and patient plasma are clotted ith n EXCESS amount of thrombin

Question 16

reagents in a fibrinogen assay

Answer 16

• standard
• thrombin
• control plasma
• *reconstitute according to instructions**
• test plasma
• Owren’s Veronal buffer (pH 7.35)

Question 17

T or F. Samples with high fibrinogen concentrations will have short clotting times

Answer 17

T

• further dilute such plasmas (120 total), repeat test and multiply graph reading by 2
• very low fibrinogen concentrations require less dilution

Question 18

how can thrombin be prevented from acting on fibrinogen

Answer 18

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

Question 19

testing for FVIII deficiency is based on …

Answer 19

the PTT method

Question 20

how does a FVIII specific assay work?

Answer 20

• 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

Question 21

decrased FVIII

Answer 21

• hemophilia
• vWD
• DIC
• liver disease

Question 22

increased FVIII

Answer 22

• inflammation with increased acute phase reactant

- immediately following surgery

Question 23

primary fibrinolysis

Answer 23

• high levels of plasmin
• unopposed by antiplasmins
• circulating fibrinogen cleaved by plasmin = FDPs

Question 24

secondary fibrinolysis

Answer 24

• 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

Question 24

secondary fibrinolysis

Answer 24

- 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

Question 25

this test is helpful in distinguishing between primary and secondary fibrinolysis

Answer 25

D-dimer test

Question 26

thrombolytic therapy required by patients with...

Answer 26

potentially life-threatening clots such as DVT, PE, and blocked coronary arteries

Question 27

difference between anticoagulant therapy and thrombolytic therapy

Answer 27

- anticoags = prevent inappropriate clotting - thrombolytic therapy = dissolve existing clots > streptokinase, urokinase, rTPA > promote generation of plasmin for clot lysis = thrombin time to monitor

Question 28

why is thrombin time useful for monitoring thrombolytic therapy

Answer 28

- 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

Question 29

compared to thrombin time, this is a more specific indicator of clot lysis

Answer 29

D-Dimer test | - recognizes fragments form cross-linked fibrin degradation

Question 30

D-Dimer Test

Answer 30

latex particles coated with monoclonal antibody to D-Dimer (mouse anti-human D-dimer) will specifically detect D-dimers in test plasma

Question 31

test sample for D-Dimer test

Answer 31

fresh, citrated, EDTA or heparinized plasma

Question 32

Notes for D-Dimer Test

Answer 32

- 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

Question 33

increased levels of D-Dimers are seen in:

Answer 33

- DVT - PE - DIC - hemorrhage - surgical patients - cancers and cirrhosis

Question 34

what is thrombin time?

Answer 34

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)

Question 35

a prolonged TT may be due to

Answer 35

- decreased levels of fibrinogen (acquired or inherited) - abnormally functioning fibrinogen - thrombin inhibitors (FDPs, heparin)

Question 36

FXIII

Answer 36

converts hydrogen bonds b/w fibrin monomers to covalent bonds

Question 37

FXIII screening test

Answer 37

- 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)

Question 38

abnormal clot solubility (disappearance of clots) seen in

Answer 38

- inherited lack of FXIII (or abnormal) - DIC - liver disease

Question 39

what are potential complications for DVT?

Answer 39

- amputation - chronic illness => post-thrombotic sybdrome - could dislodge and travel to lungs = PE (fatal if large and blocks blood flow to lungs)

Question 40

in those at risk for DVT, how can it be prevented?

Answer 40

- compression socks - healthy diet - no smoking - anticoags therapy - adequate hydration for fluid blood - exercise

Question 41

two substances responsible for a prolonged thrombin time, but do not affect fibrinogen

Answer 41

- heparin - FDP * *thrombin in excess in fibrinogen assay**