Why are platelet function tests done?Screen at-risk pre-surgical patients to determine whether they are likely to bleed excessively during an invasive procedure. Doctors currently evaluate a patient for known risk factors and rely on a patient’s clinical history and secondary hemostasis (
PT and
PTT) to determine their overall risk of excessive bleeding. There is no good platelet function screening test to predict which patients are likely to bleed during surgery.
Identify and help diagnose platelet dysfunction in those with a history of excessive bleeding. This may be someone with nosebleeds, heavy menstrual bleeding, excessive bleeding during dental procedures, etc. It is in this area that platelet function tests are of the most use. They can be used to screen for dysfunction and, along with other bleeding disorder tests such as platelet aggregometry, to help diagnose inherited and acquired platelet dysfunctions. Von Willebrand’s disease, for instance, is the most common inherited platelet dysfunction. It is associated with decreased production or dysfunction of von Willebrand factor and results in reduced adherence to the injured blood vessel and increased blood loss (most patients do clot eventually but it is a much slower process). Other inherited disorders cause decreased platelet aggregation and may include: Glanzmann’s thrombasthenia, Bernard-Soulier syndrome, and storage pool disease. Acquired platelet dysfunction may be chronic – such as can be seen with kidney failure (uremia) and myeloproliferative disorders – or temporary, such as due to medications like aspirin and nonsteroidal anti-inflammatory drugs.
Monitor anti-platelet therapy given to some patients after a stroke or heart attack to help inhibit blood clotting. Currently, most anti-platelet therapies cannot be routinely monitored with platelet function testing. An exception to this is abciximab, which can be monitored with the VerifyNow® IIb/IIa assay. As more anti-platelet therapies are created, it is anticipated that additional methods will be developed to monitor them.
Detect aspirin resistance. Low dose aspirin is being prescribed to many patients who have had a cardiovascular incident, as an anti-platelet therapy. Some of the patients on this therapy who do have another heart attack are thought to have aspirin resistance. At the moment aspirin resistance is a somewhat nebulous term – with no consensus on its definition, how many people are affected by it, on how best to measure it, whether testing can predict what will happen in an individual patient, whether the resistance will persist or be transient, whether it is also associated with resistance to other anti-platelet therapies such clopidogrel (Plavix), and with no consensus on how to alter therapy to address it. Many do not recommend testing for aspirin resistance at the moment and/or see it primarily as a research tool. Most agree that there is still much work to be done on determining its clinical relevance. A few doctors are attempting to identify aspirin resistance in their patients by ordering one or more of a variety of platelet aggregation testing methods.
Monitor platelet function during cardiopulmonary bypass surgery and cardiac catheterization. Those undergoing cardiopulmonary bypass surgery are given anticoagulants to keep them from clotting, resulting in an increased risk of excessive bleeding. At the same time, bypassing the heart and mechanically circulating the blood activates large numbers of platelets and causes them to become dysfunctional. Counting the number of platelets in blood during cardiac surgery also helps the doctors maintain a delicate balance between bleeding and clotting. Plateletworks“ is one method that is being used by some hospitals to monitor platelet function during cardiac procedures.
