von Willebrand disease and heavy menstrual bleeding: when and how to test.

von Willebrand disease (VWD) is a common inherited bleeding disorder caused by von Willebrand factor (VWF) deficiency and is an important cause of heavy menstrual bleeding in young patients. A clinical evaluation using standardized bleeding scores helps determine when screening hemostatic testing is indicated by identifying patients with a moderate or high probability of an inherited bleeding disorder. The diagnosis of VWD is made when VWF levels are under 30 IU/dL or between 30 and 50 IU/dL when there is a positive bleeding history. Activity levels above 100 IU/dL have a high negative predictive value. Multiple factors, including stress from acute bleeding and anemia, pregnancy, and medications, can affect VWF levels, hence testing for VWD is best performed when a person's health is at its baseline level, although this is not always possible in clinical practice. Variation in assay methodologies measuring VWF activity can have a significant impact on the diagnostic evaluation, and it is important for clinicians to be familiar with the limitations of the assay used by their local or reference laboratory. Genetic testing can be useful in establishing the VWD subtype and providing accurate reproductive counseling but is not required to make a diagnosis.