Platelet aggregation is highly specific for GT, as platelet aggregation fails to occur with any agonist, except ristocetin
, where the reaction is preserved.
3] Nonstandard abbreviations: FVIII, factor VIII; PT, prothrombin time; APTT, activated partial thromboplastin time; AT, antithrombin; VWF, von Willebrand factor; VWF:Ag, VWF antigen; VWF:CB, VWF collagen binding; VWF:RCo, VWF ristocetin
cofactor activity; FVIII:C, FVIII coagulant activity; FIX:C, FIX coagulant activity; PC-chrom, protein C chromogenic; PS-act, protein S activity; PS-total, protein S total; PS-free, protein S free; PC-clot, PC clotting; [CV.
Historically, VWF activity was mostly measured using the antibiotic ristocetin
as a cofactor, which enhances the binding of VWF to the platelet GPIb receptor (42).
In patients with BTM and HBT, reduced platelet aggregation response to epinephrine, collagen, ADP and ristocetin
could be explained by a defect or an impairment in glycoprotein structure of receptors on platelet membranes.
For test-associated errors, ristocetin
cofactor was associated with the highest variability and error rate, which was at least twice that using collagen binding.
Whole blood count, peripheral blood smear, blood group, ferritin, platelet function analyzer 100 (PFA-100), prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT), fibrinogen, von Willebrand factor antigen (VWF:Ag), VWF ristocetin
cofactor (VWF:RCo), factor VIII (F Viii), and platelet aggregation assays were performed.
1] To rule out coagulopathies, a structured history, Von Willebrand factor assay and ristocetin
cofactor assay may be done if necessary.
For patients undergoing major surgery, the goal of therapy is to treat with DDAVP or FVIII concentrates to maintain ristocetin
cofactor levels between 50-100% for a period of 3-10 days and if the patient undergoes a percutaneous procedure, the length of treatment is shorter (18).
5% concentration and aggregation done by arachidonic acid without affecting platelet aggregation induced by high dose of ADP, collagen, ristocetin
, and adrenalin was defined.
In 34 patients the deficiency of vWF was later confirmed by getting ristocetin
induced platelet aggregation on mixing patient plasma with control plasma.
Efficacy and safety of the factor VIII/von Willebrand factor concentrate, haemate-P/humate-P: ristocetin
cofactor unit dosing in patients with von Willebrand disease.
The response to the following agonists are now routinely assessed by LTA in our laboratory: (a) ristocetin
(Catalogue number 5199; 15mg/ml; Helena Laboratories, Melbourne Australia), used at two or more concentrations to assess minimum and maximum thresholds (typically over the range 0.