4 Steps in the
formation of a platelet plug
anti-platelet medications is to prevent the formation of
platelet plug by preventing adhesion, activation or aggregation
of platelet dysfunction is anti-platelet medications.
of platelet function tests is to measure/monitor anti-platelet
Anti-platelet medications Mode of Action
prevents the production of Thromboxane A2.
Thromboxane A2 activates the TXA2
receptors on platelets allowing them to aggregate.
prevents platelets from binding to one another by
blocking the ADP receptor site, P2Y12.
platelets from aggregating by blocking the final site of
platelet aggregation, the GPllb/llla receptor.
be used to reliably identify patients who have recently ingested
standard) A platelet agonist is added to platelet-rich plasma (PRP)
to initiate platelet aggregation. The change in turbidity of
the PRP is a measure of the platelet function.
Platelet function in whole blood can be
comprehensively evaluated by flow cytometry
is a stable and abundant metabolite of Thromboxane A2
that has platelet aggregation properties. Aspirin inhibits the
production of Thromboxane A2. A decrease in urinary
thromboxane indicates increased platelet inhibition activity.
amount of time it takes blood drawn through a fine capillary to
block a membrane coated with collagen and epinephrine (CEPI) or
collagen and ADP (CADP).
PFA 100 uses this technology)
mechanical property of a developing clot by determining the time
until initial fibrin formation.
TEG Platelet Mapping)
system consists of the platelet function assays,
dysfunction due to aspirin. Aspirin affects platelet function
by irreversibly inhibiting an enzyme involved in the production
of Thromboxane A2 that ultimately activates the GPllb/llla
receptors involved in platelet aggregation.
The assay is
based on the ability of activated platelets to bind fibrinogen.
Fibrinogen-coated microparticles aggregate in whole blood in
proportion to the number of unblocked platelet
receptors. Light transmittance increases as activated platelets
bind and aggregate fibrinogen-coated beads. The instrument
measures this change in optical signal and reports results in
Aspirin Reaction Units (ARU)>
This is a CLIA
waived assay test.
measures platelet P2Y12 receptor blockade by Plavix. The assay
is based on the ability of activated platelets to bind
fibrinogen. Fibrinogen-coated microparticles aggregate in whole
blood in proportion to the number of unblocked platelet GPllb/llla
receptors. ADP/PGE1 is incorporated into the assay
channel to induce platelet activation without fibrin formation.
Light transmittance increases as activated platelets bind and
aggregate fibrinogen-coated beads. The instrument measures this
change in optical signal and reports results in P2Y12 Reaction
In a like
manner, a second activator, iso-TRAP (Thrombin Receptor
Activating Peptide) and fibrinogen-coated microparticles are
incorporated into a second channel for assay. The instrument
measures the change in transmittance in this channel calculates
the baseline platelet function for the sample, and reports the
percent inhibition result for the sample.
turbidimetric, whole- blood assay designed to assess platelet
function based upon the ability of activated platelets to bind
to fibrinogen coated beads.
well of the VerifyNow™ IIb/IIIa assay device contains all of the
necessary reagents to perform this analysis. Within the well is
an activator that induces the platelet to change the
conformation of the GP IIb/IIIa receptor to a form that binds
fibrinogen. Additionally, the detection well also contains
fibrinogen-coated microbeads that bind to activated GP IIb/IIIa
receptors. The GP IIb/IIIa receptors on activated platelets will
bind to the fibrinogen-coated microbeads and cross-link to other
microbeads resulting in a clearing of the beads and platelets
within the detection well. The instrument uses light
transmittance to measure the rate at which this clearing occurs
and reports results in Platelet Aggregation Units (PAU)
Use of VerifyNow in Bleeding Mgmt.
to Bleeding Time
cost-effective use of blood products
of Anti-Platelet Therapy with Aspirin, Plavix and GPllb/llla
cartridge for each assay has built in wet quality control