PRP was allowed to stand at room temperature for 30 minutes Platelet aggregation was performed by turbidometric technique on Chronolog aggregometer by adding 10 um/ml Adenosine diphosphate (ADP) and 1.25 mg/ml Ristocetin
and collagen 2 ug/ml, Epinephrine 10 um/ml in 250uL PRP in separate cuvettes.
Platelet aggregation is highly specific for GT, as platelet aggregation fails to occur with any agonist, except ristocetin
, where the reaction is preserved.
The most widely used method is turbidimetry, which measures the average platelet aggregation from the difference in optical density between platelet-rich plasma (PRP) and platelet-poor plasma (PPP), when an agonist is added as ADP, epinephrine, collagen, and ristocetin
, to name a few; as the platelets are added, they allow a greater passage of light, decreasing the optical density, yielding the result through the aggregation curves as a function of time.
PRP at 1 : 10 dilution and ristocetin
, used to induce the initial VWF-platelet binding under static conditions , are then added to the labeled VWF solution.
Laboratory evaluation confirmed type 1 VWD with ristocetin
cofactor activity of 38%, von Willebrand antigen level of 41%, factor VIII level of 60%, and a normal von Willebrand factor multimer distribution.
Von Willebrand studies were normal (Von Willebrand factor [VWF] antigen, 112 IU/dL; ristocetin
cofactor, 120 IU/dL; factor VIII [FVIII] activity, 98 IU/mL).
Further workup with coagulation studies showed decreased factor VIII, vWF antigen, and vWF: ristocetin
cofactor assay, and negative Bethesda assay, indicating acquired von Willebrand disease.
Review of her baseline laboratory studies revealed that her von Willebrand factor antigen (VWF:Ag) was 18% (normal: 41-153%), ristocetin
cofactor activity (VWF:RCo) was <20% (normal: 42-200%), and factor VIII activity was 34% (normal: 50-200%).
 ([lambda] = 1060 nm and energy 10-50 J) observed similar results--the authors showed a reduction in aggregation response to collagen, ADP, and ristocetin
All the agonists used in the platelet aggregation assays (collagen from equine tendon, adenosine diphosphate (ADP), and ristocetin
) were purchased from Helena Laboratories (Beaumont, Texas, USA).
Von Willebrand factor ristocetin
cofactor (VWF: RCo) activity was measured with an in-house assay in a aggregometer (Chronolog Aggregometer 490) that measures the rate of aggregation of platelets in the presence of VWF and ristocetin