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:
Optical Aggregation in Platelet-Rich-Plasma
Selected profiles of the aggregation curve in platelet-rich plasma obtained using several agonists at different concentrations (AA: arachidonic acid; C: collagen). Click on picture to enlarge.
(Plots have been kindly provided by M. Pino. For image use, please see Use of Content at Legal Information).
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