The Multiplate device gives reproducible, precise results in volunteers and stroke/TIA patients.

Plasma levels of vWF are known to be influenced by ABO blood groups, although the mechanism remains unresolved. Group O individuals have a significantly lower level of plasma vWF than those with group A, B or AB. This relative lower level of plasma vWF may result in a bleeding tendency and a shorter half-life of infused factor VIII in group O individuals. The formation of immune complexes between vWF and autoantibodies has been shown to accelerate vWF clearance from plasma in acquired von Willebrand syndrome. However, so far no evidence has been presented that the presence of autoantibodies against vWF is involved in lowering plasma level of vWF in group O individuals. In the present study, plasma samples were obtained from 199 healthy blood donors of blood group O (50), group A (50), group B (49), and group AB (50). A time-resolved fluorescence immunoassay (TRFIA) was developed to detect anti-vWF IgG in plasma samples. Briefly, 100 μl of diluted plasma was loaded on to duplicated vWF-coated and untreated control wells of a microplate. After incubation and washing, 100 μl of Europium-labeled anti-human IgG conjugate (1:500 dilution) was added to the plate to detect vWF IgG. The time-delayed fluorescence was then measured with a Victor microplate reader (PerkinElmer, Turku, Finland). The fluorescence counts of the control wells were subtracted from those of the vWF-coated wells. The results show that anti-vWF IgG was present in all four blood groups (Table 1). Of these blood groups, group O had the highest anti-vWF IgG level with 9.8 x 105 fluorescence counts, which was 2.7- to 3.5-fold higher than that of group A, B or AB. There was a significant difference in the anti-vWF IgG levels between group O and the rest of group A, B or AB. Quantitative analysis of plasma vWF by ELISA showed that the concentration of plasma vWF of group O was 29 to 35% lower than that of group A, B or AB (Table 1). These results suggest that TRFIA is a sensitive assay for detection of anti-vWF IgG in plasma samples, and the presence of the high level of anti-vWF Ig G in group O individuals may be responsible for lowing plasma vWF by acceleration of vWF clearance. Anti-VWF IgG levels and vWF concentrations in diffeent ABO blood groups Group O (n=50) Group A (n=50) Group B (n=49) Group AB (n=50) Data are presented as a mean ± SD. *P<0.01 compared with group A, B or AB. +P<0.01 compared with group A,B or AB. Anti-vWF IgG (x 105 Fluorescence counts) 9.8 ± 6.9* 2.8 ± 2.8 3.1 ± 3.0 3.6 ± 3.5 Concentration of vWF (% of normal controls) 116 ± 42+ 165 ± 46 165 ± 42 179 ± 49