High concentrations of ADDP, the enzymes released during the release reaction, and platelet contractile proteins contribute to irreversible fusion of platelet aggregated at the site of vascular injury.
Thrombin also encourages fusion of platelets, and fibrin formation reinforces the stability of the evolving platelet plug,
PLATELET FUNCTION TEST IN IRREVERSIBLE PLATELET AGGREGATION
Platelet function tests are a group of assays that use specialized equipment to measure the ability of platelets to aggregate and promote clotting in a sample of blood. The goal of these tests is to evaluate how well platelets are doing their job in the body.
There are a variety of tests available, but no one test identified all problems with platelet function, nor is there widespread agreement on which test(s) are best for each circumstance. In addition to evaluating people for excessive bleeding, platelets function test may be used in other situations. There are conditions in which it is desirable to decrease the ability of platelets to aggregate, as in people who are at an increased risk of developing a dangerous blood clot or at increased risk for heart attacks.
These people may be prescribed medications that reduce platelet activation or reduce their ability to aggregate. People on these types of medications may have platelet function tests done as a way of monitoring their treatment.
CLOSURE TIME ASSAYS
In this test, blood is exposed to various substances that activate platelets. The blood is then drawn through a simulated wound, a small hole in a tiny tube that is coated with collagen, a protein that promotes platelet binding to wounds. In normal blood, activated platelets will bind to the coated hole, eventually plugging it.
The time required to plug the hole is measured. This is called the closure time. The longer the closure time, the lower the platelet function. This test may be abnormal if the platelet count is low, if platelet function is reduced, if other proteins needed for platelet function are reduced or if anti-platelet medications are present. This type of assay can be used to screen for Von Willebrand disease and some platelet, function disorders, but it will not detect all platelet function disorders, particularly the milder forms.
Blood clots have to be strong to stop bleeding and prevent new bleeding until healing can occur. This type of testing is designed to determine the strength of a blood clot as it forms. Substances are added to blood to start clotting while clot strength is being measured over time. Measurements are made of total clot strength; time to reach maximum strength and loss of strength over time.
These tests may be abnormal if the platelet count is low, if platelet function is reduced, or if anti-platelet medications are present. This type of testing is most often performed in large hospitals either in the operating room as a point-of-care test or in the clinical laboratory.