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Platelet Aggregation Test

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 is what stops the bleeding when you have a wound. Without platelets, you could bleed to death.

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. A lab technician will add certain chemicals to your blood sample to test how quickly your platelets form a clot.

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

Why Is the Test Performed?

Your doctor my order this test if you’re experiencing symptoms of a bleeding disorder or low platelet count. Symptoms may include:

  • excessive bleeding
  • excessive bruising
  • bleeding from the nose or gums
  • excessive menstrual bleeding
  • blood in the 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 also 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’re told otherwise, you can eat and drink before this test. You may schedule it at any time during the day, unless your doctor specifies otherwise. You shouldn’t exercise 20 minutes before your test.

A number of medications can affect the results of this test. Inform your doctor of everything you’re taking, including 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:

  • nonsteroidal anti-inflammatory drugs
  • aspirin (or medications containing aspirin)
  • antihistamines
  • antibiotics (including penicillin, cephalosporin, nitrofurantoin, and similar antibiotics)
  • tricyclic antidepressants
  • anti-platelet drugs (including clopidogrel, dipyridamole, and ticlopidine)
  • 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. You may experience mild to moderate pain while they’re drawing the blood. It may feel like a pricking or burning sensation. Relaxing your arm can help reduce the pain.

When the technician is done, they’ll remove the needle and apply pressure to the puncture to stop bleeding. You should keep pressure on the area to prevent bruising.

Your blood sample will be sent off to a laboratory for testing.

What Are the Risks?

Blood tests are considered very low-risk procedures. However, a platelet aggregation test is usually performed on people with bleeding problems. The risk of excessive bleeding is slightly higher.

If you know you have a bleeding problem, tell the technician so they’re 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 at the site of the needlestick

Speaking with Your Doctor

Call your doctor to set up an appointment if you’re experiencing excessive bleeding, bruising, or other signs of a bleeding disorder. Your doctor can assess your symptoms and determine if treatment is in order.

If your doctor decides you need a platelet aggregation test, be sure to tell them what medications you’re currently taking. This can prevent unwanted interactions and may eliminate the possibility of excessive bleeding. 

Content licensed from:

Written by: Janelle Martel
Medically reviewed on: Dec 22, 2015: Steve Kim, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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