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Heme/Lymph 1 > Laboratory Assessment and Selected Therapeutic Interventions in Hemostasis > Flashcards

Laboratory Assessment and Selected Therapeutic Interventions in Hemostasis Flashcards

1
Q

In vivo vs in vitro

A

In vivo - how it happens in the body…need to understnad for disease
In vitro - how it happens outside the body…important for understanding lab results

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2
Q

Platelet count

A

150-400 thousand/uL
Spontaneous bleeding risk low unless count is <10,000
Thrombotic risk at 1 million

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3
Q

Bleeding time

A

Standardized skin incision
Blot blood flow with filter paper until it comes away clean and measure time til it stops
Preop risk assessment for bleeding…not good

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4
Q

PFA-100

A

Superior to bleeding time
Citrated whole blood aspirated through hole in membrane lined with collagen plus epineprhine or ADP
Activated platelets aggregate
Measure time for platelet plug to occlude hole - closure time

Citrate tube sequesters calcium and only measures primar y

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5
Q

Prolonged CT

A

Thrombocytopenia, vWD, aspirin ingestion, Glanzman, thrombasthenia
not useful for antiplatelet drug monitoring
Good neg predictive value…normal CT means not primary hemostatic dz

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6
Q

PLatelet aggregation testing

A

Platelets concentrated into platelet rich plasma …various platelet activation facotrs added individually
Activation leads to GP2b/3a mediated aggregation…aggregated clumps fall out of suspension…measurable light transmission increases

Uses light transmission aggregometry

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7
Q

Impedence aggregometry

A

Whole blood…platelet aggregation increases electrical resistance

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8
Q

Glanzmann thrombasthenia on LTA

A

Will show flat line because GP2b/3a receptors don’t work and no aggregation

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9
Q

Bernard Soulier dz on LTA

A

Looks normal
Ristocetin must be used to diagnose B-S…binds to vWF and induces conformation change that exposes normally hidden GP1b binding domain, enabling it to agglutinate with platelets

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10
Q

Stoarge pool dz on LTA

A

Heterogenous

Aspirin will flatten the curve like Glanzman

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11
Q

Congenital aspirin like defect

A

Platelets do not respond to arachidonic acid

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12
Q

Aggregation vs agglutination

A

Aggregation - depends on GP2b/3a

Agglutination - depends on GP1b

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13
Q

Aspirin affect on platelets

A

Aspirin irreversibly inhibits platelet COX enzymnes and blocks TXA2 production…inihibits TXA2 mediated platelet activation

Transfers its acetyl group to the COX 1 enzyme

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14
Q

GP2B/3a antagonists

Phosphodiesterase inhibitors

A

GP2B/3a antagonists - block platelet aggregation

Phosphodiesterase inhibitors promote persistance of cyclic AMP and GMP, enhancing platelet inhibitory NO effects

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15
Q

THienopyridines

A

Block platelet activation (clopidogrel and prasugrel)

Permanently bind P2Y12 ADP receptors

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16
Q

VerifyNow

A

Rapid test for aspirin or plavix effect on patients
Employs fibrinogen coated beads whcih aggregate in proportion to GP2B/3A receptors (fewer exposed if more blocked by drug)
Agonist (ADP for plavix and AA for aspirin) activates platelets, exposing GP2B/3S which binds the beads

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17
Q

Ristocetin cofactor activity

A

Test for vWF (%)
Patients native platelets removed and replaced with formlain treated reagent platelets

Formalin treated will agglutinate at rate proportional to concentration

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18
Q

ELISA assay for vWF

A

Uses anti-vWF ABs to quantitate amount

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19
Q

Types of vWD and quantitation

A

1 and 3 - decreased vWF production…protein quantity and activity low
Type 2 - abnormal that may or may not be decreased…activity low but amount may be normal

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20
Q

RIPA

A

Ristocetin induced platelet aggregation - test for type 2B vWD
Should agglutinate at lower concentrations if type 2B because conformation already present
Test for type 2B

If diagnosed, can treat with DDAVP

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21
Q

Multimer analysis

A

Good for vWD
Type 1 and 3 - decrease in all sizes
Type 2 - selective loss of HMW multimers
TTP - increased multimer

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22
Q

Clot based test advantages and disadvantages

A

Well established, available, simple, cheap, familiar

Potentially misleading

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23
Q

Clot based tests

A

Being with platelet poor plasma…excess calcium neutralizes citrate…reagnet phospholipid fills role of removed platelets…clot formation stimulated with an agonist…end point is initial detection of clot

Only for secondary hemostatic dz

24
Q

Endpoint of clot based tests

A

Fibrinogen to fibrin cleavage (detecting fibrin formation)

25
Where do in vitro and in vivo converge?
Factor 10
26
Common pathway sequecne
10, 2 ,1
27
Extrinsic pathway
Tissue factor, F7, F10, 2, 1
28
Intrinsic pathway
F12 forms with HMWK and PK...F12 cleaves F11...F11 cleaves F9 (needs F8)...cleaes F10...2, 1
29
PTT | PT
``` Isolated PTT (partial thromboplastin time) prolongation points to extrinsic Isolated PT (prothrombin time) pointed to F7 ```
30
PTT
Partial thromboplastin time All elements intrinsic to ciruclation (No TF) TO start, silica added with Ca and phosphlipids removed Phospholipids without TF - partial thromboplastin Commonly used for monitoring unfractionated heparin
31
PT
Prothrombin time Evaluates extrinsic pathway TF needed to start the reaction...added with Ca and phospholipids previously removed Phospholipids plus TF - thromboplastin Common used for warfarin dosing
32
INR
International normalized ratio Intended to standardize PT results across labs Used for warfarin
33
Warfarin
Requires frequent labs | Dose affected by Vit K intake, drug effects of CYP2C9 metab, genetic polymorphisms of CYP2C9 and VKO reductase activity
34
If needed to start warfarin early for thromboembolism, must
Bridge with heparin due to short half life of F7...if started on full warfarin, would run out of protein C and become hypercoagulable...risk is warfarin induced skin necrosis
35
ISI
International sensitivity index - closer to 1 is better
36
INR formula
(PT patient/PT normal)^ISI | Range should be 2-3
37
PT and PTT mixing studies
How to tell if due to deficiency or inhibitor If PT/PTT corrects into the normal range, then due to factor def If not, due to inhibitor like LAC or factor specific AB
38
SPecific factor assays
Plasma deficienct in the specific factor of interest is added to patient speciemn...in absence of inhibitor, degree of prolongation inversely correlates with factor activity
39
Urea clot lysis
Used to test for F13 def | urea will lyse a clot of uncrosslinked...will not lyse clot of cross linked
40
Factor def
Single factor - mild hemophilia, if F12, then doesn't matter Multiple factors - liver dz or vit K def
41
Inhibitors
Heparin LAC Specific factor inhibitoras
42
In mixing study, if mix corrects
Need to obtain factor activity levels | If it doesn't correct, rule out heparin exposure or contam, and consider LAC testing
43
Most factor specific antibodies at
Anti-F8 - bethesda unit score...put in human plasma until 50% F8 emerges...inverse is BUS
44
LAC testing
IN vitro clotting time prolonged Mixing study does NOT correct Add excess of phospholipid and if it corrects, then lupus anticoagulant and repeat in 8-12 weeks
45
DRRVT
Dilute Russell viper venom time | Tests for LA subtypes...anti-beta-2 glycoprotein...more specific for clinically signifant LA
46
What does DRVV do?
Acvtiates F10 to initiate clotting and bypasses both intrinsic and extrinsic pathways...If LAC present, prolongs clot time
47
ACA testing
ELISA based assay | Cardiolipin Ag bound to sides of test tube...binds, detected using anti-human-Ig ABs
48
Heparin
Liver, gut, basophils, mast cells Heparin has super negative charge Chemically similar to heparans found on endothelial cells walls All heparins have a common pentasaccharide sequence that fits into AT
49
Heparin types
UFH - unfractionated heparin - range of molecular sizes with up to 30 additional sugars LMWH - low molecular weight heparin - only smaller Fondaparinux - only the pentasaccharide
50
Effect of heparin molecular size
Inhibition of thrombin requires a larger heparin molecule to span both other molecules This is not necessary for F10 inhibition Thus LMWH inhibits F10 but not thrombin
51
UFH affect
Prolongs PT and PTT
52
LMWH affect
Not reliably prolonging of PT and PTT | If needed to monitor - use anti-Xa assay
53
Anti-Xa assay
Add F10a to patient plasma...measure activity of F10...inversely proportional to heparin concentration
54
ACT
Advanced clotting time | Also a way to monitor heparin
55
Protamine
Binds and inactivates heparin
56
D-dimer values
Elevation demonstrates prior formation of cross linked fibrin Expected to be elevated in VTE, surgery, trauma Negative predictive value in reuling out VTE in case of PE
57
Rotational viscoelastography
Thromboelastography Measures whole blood clot strength over time Can help distinguish between anatomic and coagulopathic bleeding, Can detect hypercoagulability to avert thrombosis Indentifies fibrinolysis Optimizes use of blood products and antifibrinolytic drugs

Heme/Lymph 1 (14 decks)

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