American Board of Internal Medicine (ABIM) Certification Practice Exam

What is a notable laboratory finding in von Willebrand disease (vWD)?

1. Prolonged prothrombin time (PT)

2. Normal PT with slight aPTT prolongation

3. Significantly prolonged aPTT and PT

4. Elevated PT with aPTT normal

The correct answer is: Normal PT with slight aPTT prolongation

In von Willebrand disease (vWD), the most notable laboratory finding is a normal prothrombin time (PT) alongside a slight prolongation of the activated partial thromboplastin time (aPTT). This pattern occurs because von Willebrand factor (vWF) plays a crucial role not only in platelet adhesion but also in stabilizing factor VIII, which is important in the intrinsic pathway of the coagulation cascade that aPTT measures. In individuals with vWD, the deficiency or dysfunction of vWF leads to decreased levels of circulating factor VIII, resulting in a mild prolongation of the aPTT. However, because vWF does not directly influence the extrinsic pathway, PT remains normal. It is this combination, therefore, that makes the laboratory findings distinctly characteristic of von Willebrand disease. The other laboratory findings listed do not align with the expected results in vWD. For instance, a significantly prolonged aPTT and PT would suggest more severe coagulation disorders. An elevated PT with aPTT normal would indicate conditions such as liver dysfunction or vitamin K deficiency, neither of which are characteristic of vWD. The correct interpretation of these laboratory findings is crucial for the diagnosis and management of von Willebrand disease.