Population differences in von Willebrand factor levels affect the diagnosis of von Willebrand disease in African-American women

Diagnosis of von Willebrand disease (vWD) is based on a panel of laboratory tests that measure the amount and function of von Willebrand factor (vWF), In population studies, vWF is higher in African Americans than Caucasians. Bleeding time, factor VIII activity (FVIII), vWF antigen (vWF:Ag), "vWF ac tivity" ELISA (vWF:Act), ristocetin cofactor (vWF:RCof), and ristocetin-ind uced platelet aggregation (RIPA) were measured on 123 women with menorrhagi a and 123 randomly selected control women; 70 cases and 75 controls were Af rican American. Among controls, African Americans had significantly higher levels of vWF:Ag (mean 120 vs. 102 U/dl, P = 0.017). Among all subjects, Af rican Americans had higher levels of vWF:Ag (mean 123 vs, 103, P = 0.001), vWF:Act (mean 101 vs, 89, P = 0.006), and FVIII (mean 118 vs, 104, P = 0.00 6). vWF:RCof did not differ between races (93 vs, 94 U/dl), RIPA was reduce d in African Americans (P < 0.0001). In both races, women with type O blood differed significantly from those with other ABO types in vWF:Ag, vWF:Act, FVIII, and vWF:RCof. Based on criteria of two or more tests below race- an d ABO-specific reference ranges, 6.5% of menorrhagia cases and 0.8% of cont rols were classified as having vWD, or its phenocopy. Among Caucasians, no controls and 7 cases (15.6%) were classified as affected, and in African Am ericans, 1 control(1.3%) and 1 case (1.4%) were so classified. Racial diffe rences in vWF further complicate the issues surrounding diagnosis of vWD. T he finding of increased vWF:Ag not accompanied by increased vWF:RCof has im plications for understanding the structure-function relationships of vWF. A m. J. Hematol. 67:125-129, 2001. Published 2001 Wiley-Liss, Inc.<dagger>.