Iib/Iiia Assay - Accumetrics VerifyNow User Manual

cAMP and reduce the contribution of the P2Y1 receptor on activation. This makes the
assay more specific for the effects of ADP on the P2Y12 receptor. 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; and if the P2Y12 inhibitor has produced the expected
antiplatelet effect, such aggregation will be reduced. The VerifyNow P2Y12 assay reports
the extent of platelet aggregation in P2Y12 reaction units (PRU) and percent inhibition.
PRU reports the amount of ADP-mediated aggregation specific to the platelet P2Y12
receptor, and is calculated as a function of the rate and extent of platelet aggregation in
the ADP channel. Percent inhibition (%) is the percent change from baseline aggregation,
and is calculated from the PRU result and a base result. The base result is an
independent measurement based on the rate and extent of platelet aggregation from the
thrombin receptors, specifically the PAR-1 and PAR-4 receptors. To activate platelets, the
base channel incorporates the thrombin receptors' activating peptide, (iso-TRAP) and
PAR-4 activating peptide (PAR-4 AP) for the PAR-1 and PAR-4 channels respectively.
High percent inhibition values are reported if the drug has produced the expected
antiplatelet effect.
NOTE: Refer to the VerifyNow P2Y12 package insert for information to be
considered for patients receiving anti-platelet agents.
1.1.3

IIb/IIIa Assay

The final common pathway to platelet aggregation involves binding of fibrinogen to the
glycoprotein (GP) receptor complex IIb/IIIa. The GP IIb/IIIa inhibitors block platelet
aggregation by preventing fibrinogen and other adhesion molecules (vWF) from binding to
the IIb/IIIa integrin on platelets. This in turn, interferes with the transformation of the
glycoprotein IIb/IIIa receptor complex, platelet activation, and eventual formation of a
stable platelet aggregate at the site of vascular wall injury.
The VerifyNow IIb/IIIa assay is a semi-quantitative, whole blood platelet function assay
used to measure GP IIb/IIIa receptor blockade in patients treated with abciximab or
eptifibatide. The assay incorporates the agonist thrombin receptor activating peptide (iso-
TRAP) to activate platelets, and it measures platelet function based upon the ability of
activated platelets to bind to fibrinogen. A synthetic peptide, iso-TRAP, serves as a
surrogate for thrombin and activates the platelet through the PAR-1 receptor. Fibrinogen-
coated beads aggregate in whole blood in proportion to the number of unblocked platelet
GP IIb/IIIa receptors. If IIb/IIIa inhibitors have produced the expected antiplatelet effect,
such aggregation will be reduced. The VerifyNow IIb/IIIa assay reports the extent of
platelet aggregation in platelet aggregation units (PAUs). Typically, a baseline sample can
be drawn prior to GP IIb/IIIa inhibitor administration, and the PAU result can be used as a
baseline reading for determining percent inhibition (when compared to a PAU result for a
sample drawn shortly after administering the agent). High percent inhibition values are
reported if the agent has produced the expected antiplatelet effect.
NOTE: The IIb/IIIa assay can detect platelet inhibition by tirofiban (Aggrastat
another intravenous GP IIb/IIIa inhibitor; therefore VerifyNow IIb/IIIa assay results
for these patients should be interpreted with care. A sample taken prior to
VerifyNow System User Manual Page 11
INTRODUCTION - 1
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