Platelet aggregometry involves a series
of tests performed on whole blood or platelet-rich plasma,
using several agonists (platelet activators). The agonist
is added to the suspension and a dynamic measure of
platelet clumping is recorded. Simultaneously to platelet
aggregation, luminometry test can be
performed. In that case, ATP release is assayed using
a luminescent marker.
The most common aggregation agonists are:
- Arachidonic acid: used to assess
the viability of the thromboxane pathway.
- Thrombin: reacts with several membrane
sites to induce full aggregation and secretion of
organelle contents independent of the prostaglandin
or ADP pathways.
- ADP: binds to a specific platelet
membrane receptor and causes platelet activation and
release of dense granule stored ADP. Shows biphasic
aggregation.
- Epinephrine: binds to specific
receptor and causes ADP secretion, but does not cause
aggregation in storage pool disorder or release defects.
- Collagen: Shows no primary wave
of aggregation and depends on intact membrane receptors,
membrane phospholipase pathway integrity and normal
cyclooxygenase and thromboxane pathway function.
- Ristocetin: requires vWF and intact
surface membrane including a functional vWF receptor
site (GPIb).
Typical aggregation tests using platelet-rich plasma
requires a photometer with cuvette equipped with a stir
bar and warmed to 37ºC. Aggregating agent is added
and changes of optical density are plotted to view the
aggregation curve.
The following animation is available for further details:
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