Factor XII Reduction in Sickle Cell Anemia?

Our UAB coagulation lab specialists have noticed a series of prolonged PTTs associated with reduced factor XII in specimens from our sickle cell patient clinic. We found one 24-year old reference, Gordon EM, Klein BL, Berman BW, et al. Reduction of contact factors in sickle cell disease. J Pediatr 1985; 106: 427-30, that documents a significant reduction of factor XII, prekallikrein, and high molecular weight kininogen in sickle cell anemia. Conversely, a more recent publication, Koc A, Gumruk F, Gurgey A. The effect of hydroxyurea on the coagulation system in sickle cell anemia and beta-thalassemia intermedia patients: a preliminary study. Pediatr Hematol Oncol 2003; 20: 429-34, records factor VIII and protein C reduction, but specifically excludes the contact factors. Assuming for now that what UAB has seen results from contact factor consumption, has anyone else seen factor XII reduction in sickle cell, thalassemia, or other hemolytic anemias?