A platelet function test measures the rate at which your blood clots. Physicians who are treating cardiovascular patients will often order a platelet function test to see if antiplatelet medications that have been prescribed to prevent blood clots are working at their intended level. Platelet function tests can also be used to help identify the cause of excessive bleeding or to see if bleeding is a risk during surgery.

How Does It Work?

Blood clotting is your body’s natural response to healing from an injury. Your blood begins to clot because of platelets - cell fragments in blood that clump together to prevent bleeding. Platelets cause clotting at injury sites, but they can sometimes also clump at the site of deposits of plaque - a fatty substance that builds up in your arteries and can contribute to a heart attack, stroke or other problems. For this reason, cardiovascular patients are prescribed antiplatelet medications that reduce the ability of platelets to clump together. A platelet function test can tell a physician how fast a patient’s blood clots.

In the lab, a technician follows a procedure to fill small sample chambers with blood where the clotting of platelets as it would occur in your body is simulated and measured as a function of time. The resulting information allows your physician to estimate the extent to which antiplatelet medications are working. 

How Is It Performed?

A platelet function test is like any other blood test. Having blood drawn typically only takes a few minutes. You will be asked to roll up your shirt sleeve (if necessary) and the medical professional who will be drawing the blood will swab the area where the needle will be inserted with an alcohol wipe. A rubber tube may be tied around the upper part of your arm, or you may be asked to make a fist, to make the veins stand out more and easier to access.

A needle attached to a small test tube will be inserted into your vein and blood will begin to flow into the tube. When a sample that is appropriate for the test has been gathered, the needle will be removed, and you may be asked to press on a piece of gauze placed over the insertion site. This pressure will help stop any bleeding from the tiny puncture site. A bandage will then be placed over the site where the needle was inserted.

Your blood sample will then be sent to lab technicians for analysis. You will receive information when you have the blood test as to when you can expect results.

Is It Safe?

Having blood drawn by a qualified medical professional is very safe. You will experience momentary pain when the needle is inserted, and you may experience bruising at the needle insertion site after the test is complete. If you have an allergy to latex or to any adhesives, let the person know who is drawing the blood so he or she can make any necessary adjustments.

Questions to Ask Your Doctor About Platelet Function Tests

The following questions can help you talk to your physician about having a platelet function test. Consider printing out or writing down these questions and taking them with you to your appointment. Taking notes can help you remember your physician’s response when you get home.

• Why are we testing how fast my blood clots?
• What happens next if the test reveals that my blood is not clotting at the desired rate?

Please print this list of questions here. Take them with you to the doctor and share them with friends and loved ones when you are encouraging them to see their doctors.