Hemostatis Cascade

Question 1

What are the steps of hemostasis after a vessel insult?

Answer 1

1) injury
2) local vasoconstriction - multiple mediators
3) plt plug - formed in 1-3 mins, mediated by fibrinogen, VWF, ADH
4) activation of coagulation cascade which aims to make fibrin at the site which links the plts to make a scab

Question 2

What should you know about the coagulation cascade?

Answer 2

prothrombin to thrombin
thrombin then helps fibrinogen become fibrin
and try to remember you need calcium to make the whole cascade work

Question 3

how do you screen for bleeding disorders?

Answer 3

you need to do tests for each arm of the coagulation cascade:
Intrinsic pathway - check PTT ( has more letters because there are more factors at work)
Extrinsic pathway - PT/INR
Thrombin Time - Test the common pathway
Bleeding time - qualitative plt function

Question 4

What factors are part of the intrinsic pathway? Why do I care?

Answer 4

Care because warfarin acts on these -some are vitK dependent
factors 8,9,11,12 + common pathway (10)
( Vit K ones are 2,7,9,10)

Question 5

what factor is part of the extrinsic pathway?

Answer 5

factor 7 only, however it is also vitK dependent.

For this reason the extrinsic pathway is considered faster, it only needs one factor

Question 6

What do the following tests mean?

Normal INR, abn PTT

Answer 6

Instrinsic pathway deficiency = any of factors 8,9,11,12

This is also referred to as the proximal intrinsic pathway

Question 7

What do the following tests mean : normal PTT, abn INR?

Answer 7

then your one factor of your INR/ extrinsic pathway, factor 7, is messed

Question 8

what does it mean if your test normalized with a mixing study?

Answer 8

A mixing study means you pour in factors ( eg with FFP or cryo) and see what happens. If everything normalizes, you were just missing a factor

Question 9

What if your test doesnt normalize with a mixing study?

Answer 9

then a factor inhibitor is present - doesnt matter how much of the factor is around it still wont work

Question 10

what factor is not tested normally?

Answer 10

in the common pathway, to help the fibrin clot finally stabilize, factor 13 is needed, however we rarely test for if the clot stabilizes we just look for a clot

Question 11

how do you test the extrinsic pathway?

Answer 11

you take factor 7 and tissue factor, and add Ca2++, then measure the clotting time. This test actually also tests the common pathway

Question 12

what does it mean if the INR or PT is prolonged?

Answer 12

recall the factors in that pathway: 7, tissue factor, then the common pathway stuff including 10, 5, fibrinogen.
If there is a deficiency or inhibitor of either then you need a mixing study to delineate deficiency vs inhibitor

Question 13

So what is the pTT?

Answer 13

it measures the intrinsic+ common pathway, recall this is factors 8, 9, 11, 12. The only vitK depedent one here is 9 of 2,7,9,10

Question 14

what is bleeding time

Answer 14

an assessment of qualitative plt function

Question 15

what is the difference between direct and indirect coombs tests?

Answer 15

in Direct Coombs/ DAT, you are testing for a reaction that has already happened. There are abs already on RBC surface, and you add teh coombs reagent to bind the abs tgoether, to confirm a reaction has occured.
In the inidirect method, you area adding the abs to stick to the RBCs, then adding the coombs reagent

Question 16

When do you need to use direct coombs test vs indirect coombs?

Answer 16

direct coombs = a pathology is already there in the patient ie

1) hemolytic anemia
2) ABO mismatch
3) AIHA

Indirect coombs = you want to test if a reaction will occur in your patient

1) crossmatch testing
2) blood group antibodies during pregnancy
3) Abs in AIHA

Question 17

what should you do:

the INR is normal, the PTT is high

Answer 17

• this indicates an intrinsic/common pathway issue and normal extrinsic pathway.
• factors involved = 8 9 11,12, + common
• now you should do a mixing study, which means do the test again but with a mix of pt plasma + pooled plasma (rich in factors)
• if PTT still high = inhibitor present
• if PTT normalizes = deficiency was present that you rectified with the pooled plasma

Question 18

What does it mean if: High INR, normal PTT

Answer 18

indicates issue with instrinic/common pathway = factors 7, tissue factor, factor10
-consider warfarin as an issue

Question 19

what does it mean if: high INR, high PTT

Answer 19

your whole system both intrinsic and extrinsic is messed.

Warfarin!