What are platelet function assays?
Platelets (“thrombocytes”) are cells in the blood that circulate freely until there is an injury, which attracts them to accumulate at that site as one of the first steps in the clotting process. Healing begins with hemostasis, and the platelets play a crucial initial role in a clotting/clot-dissolving cycle that is part of healing.
The four main platelet functions are
- Adherence to each other
- Taking part synergistically with other coagulation factors
When circulating platelets are exposed to tissue, as happens when injury interrupts the lining that separates them, they adhere to the tissue, which activates them to secrete factors which attract other platelets to do the same. Next, circulating fibrinogen begins to bind, and this prompts further platelet aggregation, which stabilizes the growing clot. Meanwhile, the tissue exposed to the vascular circulation signals other processes which begin additional cycles in the clotting process.
When one fails to clot effectively or when there is over-functioning of platelets that produces clots that could obstruct blood flow or embolize, one or more of the four functions above are abnormal, and platelet testing is an important tool in investigating the cause so that appropriate interventions can be made.
Although merely counting the platelets within a certain volume of blood is helpful in identifying thrombocytopenia (i.e., too few platelets, leading to bleeding), this does nothing to measure their successful function or identify their dysfunction within the body. The difficulty in evaluating platelet function as it occurs inside the body, which makes the platelet count insufficient for dysfunctional diagnoses, has been solved with recent technologies.
Platelet function assays are not only helpful in diagnosing bleeding disorders or thrombosis, but also determine the efficacy of therapy when antiplatelet drugs are used to treat a tendency toward clotting in abnormal situations.