How should I interpret laboratory results for Von Willebrand factor levels and activity in suspected cases?

When interpreting laboratory results for Von Willebrand factor (VWF) levels and activity in suspected bleeding disorders, it is essential to assess both quantitative and functional parameters to accurately diagnose and classify von Willebrand disease (VWD). Measurement of VWF antigen (VWF:Ag) provides the quantitative level of the protein, while VWF activity assays, such as ristocetin cofactor activity (VWF:RCo), evaluate the functional capacity of VWF to mediate platelet adhesion. A discrepancy between VWF:Ag and VWF activity, particularly a reduced activity relative to antigen, suggests qualitative defects typical of type 2 VWD. Normal or low-normal VWF:Ag with proportionally reduced activity may indicate type 1 VWD, a partial quantitative deficiency. Additionally, factor VIII levels should be measured as they are often reduced in VWD due to VWF’s role in stabilizing factor VIII. Interpretation must consider that VWF is an acute phase reactant and can be elevated by stress, inflammation, or pregnancy, potentially masking deficiencies. Therefore, repeat testing or testing in a steady state may be necessary. The integration of these laboratory findings with clinical bleeding history is critical for accurate diagnosis and sub-classification, guiding appropriate management ¹ (Favaloro, 1999).