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1.1.1
Aspirin Assay
Acetylsalicylic acid (aspirin) has a significant antiplatelet effect by blocking the production
of thromboxane A2. A potent platelet agonist, thromboxane A2 is released by activated
platelets and acts to cause vasoconstriction and amplify platelet recruitment by binding to
thromboxane receptors on the surface of circulating platelets. In an activated platelet,
arachidonic acid is converted by cyclo-oxygenase (COX-1) to prostaglandin G
and PGH
and then to thromboxane A2. Aspirin affects platelet function by irreversibly
2
inhibiting the cyclo-oxygenase (COX) activity of prostaglandin (PG) H-synthase, which in
turn blocks the metabolism of arachidonic acid to thromboxane A2 (TXA2). The primary
pharmacological effect of aspirin on platelets is to decrease the activation of the GP
IIb/IIIa receptor and activation of other platelets.
VerifyNow Aspirin assay is a qualitative test to aid in the detection of platelet dysfunction
due to aspirin ingestion in whole blood for the point-of-care or laboratory setting. The
assay incorporates the agonist arachidonic acid to activate platelets, and it measures
platelet function based upon the ability of activated platelets to bind to fibrinogen.
Fibrinogen-coated microparticles aggregate in whole blood in proportion to the number of
activated platelet GP IIb/IIIa receptors. If aspirin has produced the expected antiplatelet
effect, such aggregation will be reduced. The VerifyNow Aspirin assay reports the extent
of platelet aggregation as aspirin reaction units (ARUs). Given an ARU range of 350-700,
ARU values less than 550 are consistent with aspirin-induced inhibition of platelet
function, whereas values greater than or equal to 550 ARUs are not consistent with
aspirin-induced inhibition.
NOTE: The Aspirin assay is not for use in patients with underlying congenital
platelet abnormalities, patients with non-aspirin induced acquired platelet
abnormalities or in patients receiving non-aspirin anti-platelet agents. Refer to the
VerifyNow Aspirin package insert for information to be considered for patients
receiving NSAIDS. The Aspirin assay may be used in patients treated with
selective COX-2 inhibitors, e.g. celecoxib (Celebrex
1.1.2
P2Y12 Assay
P2Y12 inhibitors (e.g. thienopyridines) are a class of therapy that has significant
antiplatelet effect by inhibiting adenosine diphosphate (ADP)-mediated platelet activation.
Platelet activation by ADP plays a key role in the development of arterial thrombosis.
When secreted by activated platelets from storage granules, the ADP activates additional
platelets in circulation through two G protein-coupled P2 receptors, P2Y1 and P2Y12.
P2Y12 inhibitors irreversibly inhibit ADP binding to the P2Y12 receptor on the platelet
surface. By blocking this receptor, these agents interfere with additional platelet
activation, degranulation, and - by inhibiting the modification of the glycoprotein IIb/IIIa
receptor— aggregation.
The VerifyNow P2Y12 assay is a whole blood assay used in the laboratory or point of care
setting to measure P2Y12 receptor blockade. The assay incorporates the agonist ADP to
activate platelets. The VerifyNow P2Y12 assay also uses PGE1 to increase intraplatelet
VerifyNow System User Manual
®
).
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INTRODUCTION - 1
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