ITC VerifyNow System Platelet Reactivity Test - Manual (Page 9)

Page 5 14439.C 03/2013
Introduction - 1
VerifyNow System User Manual | USA
1.1.3 IIb/IIIa Test
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 Test is a semi-quantitative, whole blood platelet function test used to measure
GP IIb/IIIa receptor blockade in patients treated with abciximab or eptifibatide. The test 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 Test 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 Test can detect platelet inhibition by tirofiban (Aggrastat ® ), another intravenous GP IIb/IIIa inhibitor;
therefore VerifyNow IIb/IIIa Test results for these patients should be interpreted with care. A sample taken prior to abciximab
or eptifibitide administration cannot be used to establish a “baseline” or uninhibited result if a GP IIb/IIIa inhibitor was
administered within the past 10 days.
1.2 Test Procedure
The VerifyNow System has been developed to provide a simple, accurate and reliable means to
measure platelet aggregation. This section provides an overview of the test procedure.
Whole blood is collected from an indwelling catheter or from a peripheral site into a vacuum collection
tube. If collected into a syringe, transfer blood to the blood collection tube immediately after collection.
The tube is gently inverted five times and stored at room temperature until use (up to 4 hrs, depending
on the test type). Refer to Chapter 6, Patient Testing for more information on sample collection.
At the start of the test, the test device is inserted into the instrument, and the sample collection tube is
gently inverted again several times and placed on the test device, requiring no cap removal, specimen
preparation, or pipetting step. The instrument automatically draws the sample from the vacuum
collection tube into the test device, and proceeds with the analysis of the sample. The used device and
tube are removed and discarded. There is no blood handling required by the user. Results are reported
within 2-5 minutes, depending on the test.
Refer to Chapter 5, Quality Controls and Chapter 6, Patient Testing for more information on operating
the instrument.