Platelet Aggregation Test

Written by Janelle Martel | Published on July 9, 2012
Medically Reviewed by George Krucik, MD

Platelet Aggregation Test

A platelet aggregation test checks how well your platelets clump together. Platelets are types of blood cells. They help form blood clots by sticking together. A clot stops the bleeding when you have a wound.

A platelet aggregation test requires a blood sample. The sample will be examined to see how the platelets are distributed through the plasma. Plasma is the liquid part of the blood. The lab technician will also add certain chemicals to your blood sample to test how quickly your platelets form a clot.

This test may also be called an aggregometer test or a platelet aggregation assay.

Why Is the Test Performed?

This test may be ordered if you are experiencing symptoms of a bleeding disorder or low platelet count. Such symptoms may include:

  • excessive bleeding
  • excessive bruising
  • bleeding from the nose and gums
  • heavy menstrual bleeding
  • blood in urine or stool

Your doctor may also order this test if you have a family history of bleeding problems.

The results of this test can help your doctor figure out the cause of bleeding problems. It can be used to help diagnose:

  • an autoimmune disorder (such as lupus)
  • genetic disorders (including Bernard-Soulier syndrome, Von Willebrand disease Glanzmann’s thrombasthenia, or platelet secretion disorder)
  • medication side effects (that affect platelet formation or degradation of fibrin, an important clotting protein)
  • myeloproliferative disorders (which cause blood cells to overgrow)
  • uremia (a condition caused by kidney failure)

How to Prepare for the Test

Unless you are told otherwise, you can eat and drink before this test. You may also schedule it at any time during the day, unless your doctor specifies otherwise. However, you should not exercise in the 20 minutes prior to your test.

A number of medications can affect the results of this test. Inform your doctor of everything you are taking, including both over-the-counter and prescription drugs. Your doctor will tell you if you should stop taking a drug or change the dosage before your test. Medications that can interfere with a platelet aggregation test include:

  • non-steroidal anti-inflammatory drugs (NSAIDs)
  • aspirin (or medications containing aspirin)
  • antihistamines
  • antibiotics (including penicillin, cephalosporin, nitofurantoin, and similar antibiotics)
  • tricyclic antidepressants
  • anti-platelet drugs (including clopidogrel, dipyridamole, and ticopidine)
  • theophylline (a medication used to relax airway muscles)

What Happens During the Test

A platelet aggregation test requires a blood sample. The sample may be taken at a doctor’s office or a medical laboratory.

To begin, the technician will put on gloves and clean the area around your vein. Blood is usually drawn from a vein on the inside of the elbow or the back of the hand. Next, the technician will tie an elastic band around your upper arm. This helps the blood collect in your vein. It makes it easier to draw blood. The technician will insert a sterile needle into your vein and draw blood. The elastic band will be removed from around your arm.

You may experience mild to moderate pain while blood is being drawn. It may feel like a pricking or burning sensation. Relaxing your arm can help reduce the pain.

When the technician is done, he or she will remove the needle and apply pressure to the puncture to stop bleeding. A bandage will then be applied. You will be told to keep pressure on it to help prevent bruising. Your blood will be sent off to a medical laboratory for testing.

What Are the Risks?

Blood tests are considered very low-risk procedures. However, a platelet aggregation test is usually performed on individuals with bleeding problems. Therefore, there is a slightly higher than usual risk of excessive bleeding.

If you know you have a bleeding problem, tell the technician so that he or she is prepared. You should also inform the technician if you have experienced dizziness, fainting, or nausea during a previous blood test.

Possible risks of a blood draw include:

  • multiple puncture wounds (due to trouble finding a vein)
  • feeling lightheaded or fainting
  • excessive bleeding
  • hematoma (a collection of blood under the skin)
  • infection
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