To help determine the cause of or potential for excessive bleeding, to monitor and evaluate platelet function, and to monitor the presence and effectiveness of antiplatelet medications
Platelet Function Tests
Platelet Function Tests
Também conhecido como
Platelet aggregation studies
PFT
Platelet function assay
PFA
Nome formal
Platelet Function Tests
Este artigo foi revisto pela última vez em
Este artigo foi modificado pela última vez em 10 de Julho de 2017.
At a Glance
Why Get Tested?
When To Get Tested?
When you are bruising easily or experiencing excessive bleeding, when you are taking medications that can alter platelet function, and prior to or during certain surgeries
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
You may be instructed to refrain from taking drugs that can affect the results of these tests, such as aspirin, non-steroidal anti-inflammatory drugs (NSAIDs), or any over-the-counter medications that contain drugs such as these. The most common NSAIDs include ibuprofen, naproxen and COX-2 inhibitors.
Accordion Title
Common Questions
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How is it used?Various platelet function tests are used to evaluate the ability of platelets to clump together and begin to form a clot. They may be used for a variety of reasons. Examples of some of the situations they may be used include:
- To identify and help diagnose platelet dysfunction in those with a history of excessive bleeding. 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 disease, for instance, is the most common inherited platelet dysfunction. It is associated with decreased production or dysfunction of Von Willebrand factor (VWF) and results in reduced platelet adherence to the injured blood vessel and increased blood loss.
- To monitor anti-platelet therapy given to some patients after a stroke or heart attack to help inhibit blood clotting. Currently, most anti-platelet therapies are not routinely monitored with platelet function testing. As more anti-platelet therapies are created, it is anticipated that additional methods will be developed to monitor them.
- To detect aspirin resistance. Low dose aspirin is being prescribed as an anti-platelet therapy to many people who have had a cardiovascular incident, such as heart attack or stroke. Some of those 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 person, 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 platelet function tests.
- To monitor platelet function during complex surgical procedures including cardiopulmonary bypass surgery, cardiac catheterization, liver transplantation, and trauma surgery. 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.
- To screen at-risk pre-surgical patients to determine whether they are likely to bleed excessively during an invasive procedure. These include, for example, people with a prior history of bleeding problems or those on drugs that affect the ability of blood to clot, such as aspirin and non-steroidal anti-inflammatory drugs (NSAIDs). Doctors currently evaluate a person for known risk factors and rely on the person's clinical history and secondary hemostasis tests (PT and PTT) to determine the overall risk of excessive bleeding. There is no single platelet function screening test that will definitively predict which people are likely to bleed during surgery.
Some other tests that may be done in conjunction with or as follow up to these tests to evaluate platelet disorders include CBC, platelet count, PT, PTT, and Von Willebrand factor.
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When is it ordered?One or more platelet function tests are ordered whenever a doctor wants to evaluate platelet function. This may be:
- Prior to surgery or other invasive procedure
- During surgery, especially prolonged procedures
- When a person is experiencing symptoms of platelet dysfunction, such as excessive bleeding; these include numerous nosebleeds, heavy menstrual bleeding, excessive bleeding during dental procedures, etc.
- When a person is taking a medication that can have an effect on platelet function.
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What does the test result mean?The interpretation of results of the various types of platelet function tests depends on why the test(s) were performed.
In the investigation of excessive bleeding or the potential for bleeding during surgery, abnormal results may indicate the presence of platelet dysfunction. Further testing, such as specific bleeding disorder tests or clinical evaluation is often necessary to identify an inherited disorder or acquired condition as the cause of the dysfunction.
Examples of inherited platelet function disorders include:
- Von Willebrand disease — associated with decreased production or dysfunction of Von Willebrand factor and results in reduced platelet adherence to the injured blood vessel and increased blood loss
- Glanzmann's thrombasthenia — affects platelets ability to aggregate
- Bernard-Soulier syndrome — characterized by reduced platelet adhesion
- Storage pool disease — can affect platelet ability to release substances that promote aggregation
Acquired platelet dysfunction — those that are not inherited — may be due to chronic conditions such as:
- Kidney failure (uremia)
- Myeloproliferative disorders (MPDS)
- Acute leukemia
Some acquired platelet disorders that are temporary include:
- Decreased function due to medications like aspirin and nonsteroidal anti-inflammatory drugs
- Abnormal function after prolonged cardiac bypass surgery
When a person is taking a medication that can affect platelet function, such as aspirin, then the results of testing reflect the platelet response to the medication.
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Is there anything else I should know?Platelet function testing is not a perfect reflection of the clotting process in the body (in vivo). A person with normal platelet function test results may still experience excessive bleeding or inappropriate clotting during and after a surgery.
Most samples for platelet function testing are only stable for a very short period of time. Testing choices are often limited to what is locally available.
There are several drugs that can affect the results of platelet function tests. Some of these include:
- Aspirin and aspirin-containing compounds
- Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and any over-the-counter medications that contain NSAIDs
- Tricyclic antidepressants
- Antihistamines
- Some antibiotics
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Should everyone have platelet function tests?Many people will never need to have platelet function testing performed. It is generally only indicated when someone is experiencing bleeding, on specific medications, or having certain surgeries. The tests are not indicated for general screening.
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Can my doctor choose from a variety of platelet function tests?Typically, a hospital or laboratory will offer one or more tests but not a wide variety. These tests evaluate the same thing – platelet function – in different ways. Since the sample must be tested promptly, the doctor will choose from what is available. Rarely, if a doctor wanted a particular type of test done, then it might be necessary for you to go to a clinic, hospital, or another city where that test is performed.
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Will my platelet function change over time?It could. While some conditions associated with platelet dysfunction are inherited, others are acquired and may occur at any point in your life. Platelet dysfunction that is due to a chronic disease may persist but can generally be managed. Dysfunction due to medication will typically resolve once the medication is discontinued.