Introduction; Platelet Function Testing - Accumetrics VerifyNow User Manual

INTRODUCTION - 1

Introduction
1
Before you begin to use the VerifyNow System, it is appropriate to review the purpose of the test.

Platelet Function Testing

1.1
In general, platelet function testing measures the activity of platelets. Therapies that inhibit platelet
function have been used extensively to prevent the clinical complications of atherothrombosis.
Three classes of potent anti-platelet agents, including acetylsalicylic acid (aspirin), P2Y12
inhibitors (e.g. thienopyridines), and glycoprotein (GP) IIb/IIIa inhibitors, have been developed.
One method detects platelet activity by measuring in vitro platelet aggregation in a blood sample
exposed to specific agonists. This includes inhibition of platelet activity in response to anti-platelet
therapies. The VerifyNow system is a whole blood, point-of-care assay, which measures platelet-
induced aggregation as an increase in light transmittance. It consists of a turbidimetric-based
Figure
optical detection instrument, single-use assay devices, and associated quality controls (
1-1
).
Figure 1-1 VerifyNow System
There are three types of VerifyNow assays: Aspirin, P2Y12, and IIb/IIIa (specifically for monitoring
of abciximab or eptifibatide). Each assay device contains a lyophilized preparation of human
fibrinogen coated beads and a platelet agonist. The platelet agonist varies by assay type. Each
assay is based upon the ability of GP IIb/IIIa receptors on activated platelets to bind to fibrinogen-
coated beads. When the activated platelets are exposed to the fibrinogen-coated beads,
agglutination occurs in proportion to the number of available platelet receptors. The instrument is
designed to measure this agglutination as an increase in light transmittance. The following sections
describe the mechanism of action for the three assays. Refer to Chapter 2, Overview of System
Components for more information on the instrument and consumables.
It should be noted that GP IIb/IIIa inhibitors such as abciximab (ReoPro®), eptifibatide (Integrilin®)
and tirofiban (Aggrastat®) interfere with the VerifyNow® Aspirin and P2Y12 assays. Patients who
have been treated with Glycoprotein IIb/IIIa inhibitor drugs should not be tested with the
VerifyNow® Aspirin or P2Y12 assays until platelet function has recovered. This time period is
approximately 14 days after discontinuation of drug administration for abciximab (ReoPro®) and up
to 48 hours for eptifibatide (Integrilin®) and tirofiban (Aggrastat®). The platelet function recovery
time varies among individuals and is longer for patients with renal dysfunction. Results obtained
from patients tested prior to platelet function recovery may be inconsistent and unreliable.
The following sections describe the mechanism of action for the three assays. Refer to Chapter 2,
Overview of System Components for more information on the instrument and consumables.
VerifyNow System User Manual Page 9 14340.J