HoG Handbook

Testing and Diagnosis of VWD and Platelet Disorders


blood testBecause platelet disorders are rare and many doctors are not familiar with von Willebrand Disease , it is best to go to a Hemophilia Treatment Center (HTC) for testing.  An HTC will also have the special machines necessary to do some of the tests.  Even though it is called a Hemophilia Treatment Center, an HTC also gives expert care to people with VWD and platelet disorders.

Symptoms of a Platelet Disorder

One of the most important ways of figuring out if someone has a platelet disorder is to look at how she or he has bled in the past.  These are some of the most common symptoms:

  • Easy bruising – especially bruises that happen when you can’t remember hurting yourself, bruises on several different parts of your body, and large bruises (bigger than three inches)
  • Frequent nosebleeds – especially ones that are hard to stop
  • Gums that bleed easily

For women:

  • A monthly period that lasts longer than seven days with a very heavy flow
  • Bleeding in the stomach or intestine
  • Bleeding that is unusually heavy or takes too long to stop after an injury, surgery, dental work, or childbirth

Most people with VWD or a platelet disorder have very mild symptoms.  They may not realize that they have a disorder unless they have surgery or are badly injured.  Some people, though, will have frequent bleeding that greatly affects their lives.

The doctor or nurse will want to know if other people in your family have had problems with bleeding.  She or he will also ask you about drugs and herbs you are taking that may affect your platelets.  A list of drugs and herbs that can affect platelets can be found here.

Tests for VWD and Platelet Disorders

To determine if you have a bleeding disorder and what type it might be, the doctor will order blood tests.  These are some of the blood tests used to diagnose VWD and platelet disorders:

  • Platelet Count – The number of platelets in a cubic millimeter of blood is counted.  The normal amount is between 150,000 and 450,000.
  • Platelet Aggregation Testing – The platelets from a blood sample are put into tubes.  Then different chemicals are added to the tubes to see if they make the platelets stick together (aggregate).  A machine is used to detect this.  The chemicals used are ones that make normal platelets stick together.  These chemicals are called agonists.  An important one is an antibiotic called ristocetin.
  • Bleeding Time – In the past, one of the most common tests for a platelet disorder was the bleeding time.  To do this test, a blood pressure cuff is put on your upper arm.  It is inflated to a certain pressure.  Then a device is put on your forearm that makes a small, usually painless, cut.  A stopwatch measures how long it takes for this cut to stop bleeding.  Many doctors no longer use this test.  It is difficult to standardize.  This means that the way one person does the test may be slightly different from the way another person does it.  That makes it difficult to compare the test results.  Also, the bleeding time is often normal in people even though they have a platelet disorder.
  • PFA-100® – The PFA 100® is a machine that can test how well platelets can stick and clump together.  It does this under conditions like those found inside the body when a blood vessel is torn.  It measures how long it takes a blood sample to form a platelet plug.  The result is called the Closure Time (CT) and is measured in seconds.
  • Electron Microscopy – By looking at platelets under a powerful electron microscope, a doctor can tell if they have a normal shape.  The microscope can also reveal if the storage granules inside the platelet are normal.