Larry
Forum Newbie
Topics: 8
Posts: 21
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Hi, guys,
Your answer is greatly appreciated.
They share
1. Normal Plt cout.
2. BT increased.
3. Normal PT, PTT. (the VWD is the type without low factor 8)
4. Reduced Plt aggregation.
How can tell them apart?
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| doc4mindia
Forum Guru
Topics: 134
Posts: 243
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In Von Willebrand's disease, platelet aggregation studies with standard agonists (ADP,collagen,thrombin) are normal but platelet aggregation in response to ristocetin may be sub normal.
In Glanzmann's Thrombasthenia, platelets fail to aggregate in response to typical agonists (ADP,collagen,thrombin) but aggregate normally in response to ristocetin.
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| Larry
Forum Newbie
Topics: 8
Posts: 21
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Is Von Willebrand factor is just ristocetin cofactor?
Could you please clearly define each of them?
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| fried water
Forum Junior
Topics: 4
Posts: 57
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hey larry,
vWFD is due to deficiency of vWF which is needed for normal aggregation of platelets. When platelet aggregation occur its like:
platelet--GP2b/3a--fibrinogen--GP2b/3a--platelet--GP1b--vWF--collagen (endothelium of vessel)
so in vWF disease the adhesion (to collagen, not aggregation) is defective. Ristocetin is not normally found in body.. it is an agent used in laboratory to make the diagnosis of vWF ds. Basically it is a lab agent to replace vWF, so that platelets could adhear normally again. If it happens so, its diagnostic for vWF ds. But i think nowdays its easier to diagnose coz if you suspect it you can always do vWF level assays in lab! And yea one more thing in vWF ds the PTT is not always normal rather it is increased because the half life of factor 8 (clotting factor 8 from intrinsic pathway) is decreased substantially from around 12 hrs in presence of vWF to around 2 hrs in its absence... this is because facor 8 normally circulates in body bound to vWF and the deficiency of vWF makes it degrade sooner.. so the PTT is usually increased... yea but if its with normal factor.. stick to above test 
 hope that helps.. thats all i remember!
PS: thrombasthenia is due to GP 2b/3a deficiency.. so here platelet aggregation is defective not adhesion to collagen. and yea with normal vWF levels and ristocetin test is negative.
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| Larry
Forum Newbie
Topics: 8
Posts: 21
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fried water,
You're awesome!
Thank you.
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| fried water
Forum Junior
Topics: 4
Posts: 57
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thank you too  !!!!!!!!!1
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| fried water
Forum Junior
Topics: 4
Posts: 57
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hey larry,
i did a mistake there.. i had to clarify it that 'ristocetin' is not to replace vWF but it works as collagen in lab.. and in vWF ds platelets wont adhear to it.. so ristocetin test is abnormal in vWF ds.
---sorryyyyy!!
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| tess
Forum Guru
Topics: 131
Posts: 368
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Nice discussion.
Is it correct:
In both disease, we have normal platelet count, but in
1) Von Willebrand's disease, there is inc PTT and also bleeding time
2) Glanzmann's Thrombasthenia, there is inc bleeding time only, PTT is normal.
Thanks for feedback!
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