Diagnosing von Willebrand Disease

Screening tests

A combination of blood tests is needed to diagnose von Willebrand disease (VWD). The following screening tests are done first to show if the blood is clotting properly. These tests may suggest a possible bleeding disorder, but more tests are needed to tell the type of bleeding disorder present. Screening tests are often normal in VWD, and more specific tests are required.

Complete blood count (CBC)

This common test measures the amount of hemoglobin (the red pigment inside red blood cells that carries oxygen), the size and number of red blood cells, and the numbers of different types of white blood cells and platelets found in blood. The CBC is normal among people with VWD. However, if a person with VWD has unusually heavy bleeding or bleeds for a long time, the hemoglobin and the red blood cell count can be low.

Activated partial thromboplastin time (APTT) test

This test measures how long it takes for blood to clot. It measures the clotting ability of factors VIII (8), IX (9), XI (11), and XII (12). If any of these clotting factors is too low, it will take longer than normal for the blood to clot. The results of this test will show a longer clotting time among some people with VWD. However, the results of this test will be normal among people with mild VWD.

Prothrombin time (PT) test

This test also measures the time it takes for blood to clot. It measures primarily the clotting ability of factors I (1), II (2), V (5), VII (7), and X (10). If the level of any one of these factors is too low, it will take longer than normal for the blood to clot. The results of this test will be normal among most people with VWD.

Fibrinogen test

This test also helps doctors assess a patient's ability to form a blood clot. This test is ordered either along with other blood clotting tests or when a patient has an abnormal PT or APTT test result, or both. The results of this test will be normal among people with VWD. Fibrinogen is another name for clotting factor I (1).

Diagnostic tests

Specific tests are required to diagnose which bleeding disorder is there. Often these tests need to be repeated several times before an accurate diagnosis can be made. This is because the levels of clotting factors in the blood vary over time as a result of changes the body might be reacting to―such as stress, pregnancy, and infections―that can affect the test results.

The blood tests that a doctor can order to diagnose VWD (or another platelet disorder) include:

• Factor VIII clotting activity―To measure the amount of factor VIII in the blood
• Von Willebrand factor antigen―To measure the amount of VWF in the blood
• Ristocetin cofactor or other VWF activity―To measure how well the VWF works
• Von Willebrand factor multimers―To measure the makeup or structure of the VWF
• Platelet aggregation tests―To measure how well the platelets are working