When evaluating a patient for von Willebrand disorder, the ABO blood type that has the lowest level of vWF is which?

When evaluating a patient for von Willebrand disorder, the ABO blood type that has the lowest level of vWF is which?

• A. O
• B. A
• C. B
• D. AB

Answer: (A)

The question hinges on how ABO blood type affects circulating von Willebrand factor. Among the blood groups, type O has the lowest baseline von Willebrand factor levels. Von Willebrand factor carries and stabilizes factor VIII and promotes platelet adhesion, so its level in plasma influences bleeding tendency. ABO antigens on vWF influence its stability and clearance from the bloodstream, with non-O types (A, B, AB) having higher vWF levels than type O. Because type O individuals have inherently lower vWF, this can affect interpretation of vWD tests, since a low vWF level might appear more pronounced in someone with type O even if they don’t have von Willebrand disease. Therefore, the blood type with the lowest vWF is type O.

The question hinges on how ABO blood type affects circulating von Willebrand factor. Among the blood groups, type O has the lowest baseline von Willebrand factor levels. Von Willebrand factor carries and stabilizes factor VIII and promotes platelet adhesion, so its level in plasma influences bleeding tendency. ABO antigens on vWF influence its stability and clearance from the bloodstream, with non-O types (A, B, AB) having higher vWF levels than type O. Because type O individuals have inherently lower vWF, this can affect interpretation of vWD tests, since a low vWF level might appear more pronounced in someone with type O even if they don’t have von Willebrand disease. Therefore, the blood type with the lowest vWF is type O.