Dear George, I am a student and I would like to ask for your help regarding a platelet aggregometry question. If the graph shows no reaction to the agonists ADP, epinephrine and ristocetin what does that mean? Thank you. Maria Carmis.
Hello, Maria, and thank you for your question. If you happen to be using the textbook,Rodak BF, Fritsma GA, Doig K. Hematology Clinical Principles and Applications, 3rd Edition, the answer can be derived from pages 679 to 681.
ADP and epinephrine depend upon intact membrane receptor sites, P2Y1 and P2Y12 for ADP and an α-adrenergic site for epinephrine. They also depend upon functional platelet activation pathways, so a membrane receptor defect or a platelet activation pathway defect, which is also called a secretion defect or aspirin-like disorder can result in no aggregation. You’ll need to compare to arachidonic acid and collagen results to sort out the differences, and ensure the patient has not taken aspirin.
Ristocetin is the agonist used to detect von Willebrand disease, and a negative response is presumptive, but not conclusive for this common bleeding disorder. The ristocetin test is not very sensitive, and most laboratories choose to use the ristocetin cofactor assay or the collagen binding assay to screen for von Willebrand disorder. Von Willebrand disease is not actually a platelet defect, it is a deficiency of the plasma protein, von Willebrand factor, and platelets in von Willebrand disease respond normally to the other agonists. The combination of poor response to ADP, epinephrine, and ristocetin together can only lead to a multiple conclusion. I hope this is helpful. Geo