Platelet Aggregation
Platelet aggregation testing is considered to be the "Gold Standard" of platelet function analysis. The Hemostasis and Thrombosis Laboratory uses a technique known as lumi-aggregometry which can be performed on whole blood using the principle of electrical impedance. This technique has the advantage of speed, use of a more physiological test sample (whole blood) and a full panel of agonists can be run on two blue top tubes (10 ml).
An electrode is immersed in the blood sample under test. Platelets naturally adhere to the probe and quickly form a stable monolayer. When an aggregating agent is added, the platelet aggregates form on the electrode (shown below) and increase the resistance to a current being applied across the electrode The instrument monitors the change in electrical impedance which reflects the platelet aggregation response.
In addition, we simultaneously monitor the release of ATP from the aggregating platelets by a technique known as luminescence. This allows us to detect the presence of platelet release reaction disorders and storage pool defects affecting the platelet dense granules.
The rate and extent of both platelet aggregation and release are monitored for 6 minutes. Aggregation is routinely measured in response to ADP, collagen, arachidonic acid and ristocetin (1.0 and 0.5 mg/ml), while ATP release is measured following addition of thrombin, ADP, collagen and arachidonic acid.
Although quantitative results are obtained for each agonist, these are not generally reported to the physician. Dr. Francis personally reviews the various aggregation and release curves and provides a written interpretation on all tests.
It should be noted, that because the test is performed on whole blood, thrombocytopenia may give abnormal platelet aggregation and release patterns.
Unless the purpose of the test is to demonstrate a medication-induced platelet defect, platients should refrain from all medications (e.g. aspirin, Plavix, Abciximab, etc.) and vitamin or herbal supplements (e.g. fish oil, caffeine, garlic, ginseng, vitamin E, ginger, Ginko Biloba etc.) known to interfere with platelet function, for at least 7 days prior to testing.
