Why von Willebrand disease has normal aPTT sometimes ?

VWF acts as a carrier protein for factor VIII.  Factor VIII is more rapidly degraded when unbound, and VWF deficiency can therefore lead to impairment of the intrinsic coagulation pathway leading to a prolonged activated PTT.  

However, patients can have a normal aPTT for a variety of reasons:

• Patients with mild to moderate VWF deficiency may have adequate factor VIII levels to maintain aPTT within normal range (most common reason)

• VWF and factor VIII are acute-phase reactants; stress and inflammation can acutely raise levels

• VWF synthesis is increased by estrogen and thyroid hormones; pregnancy, oral contraceptives, and thyroid hormone replacement can raise VWF levels and normalize aPTT. 

  
  

  That’s all!

  Thank you!