LABORATORY ASSESSMENT OF VON-WILLEBRAND-FACTOR - USE OF DIFFERENT ASSAYS CAN INFLUENCE THE DIAGNOSIS OF VON WILLEBRANDS DISEASE, DEPENDENT ON DIFFERING SENSITIVITY TO SAMPLE PREPARATION AND DIFFERENTIAL RECOGNITION OF HIGH-MOLECULAR-WEIGHT VWF FORMS

Three separate laboratory assays for von Willebrand Factor (VWF), a st andard ''antigen'' (antisera-ELISA-based) assay (VWF:AB), a standard r istocetin-dependent-platelet-agglutination procedure (VWF: RCof), and an ELISA-based collagen-VWF binding assay (VWF: (SEA), have been evalu ated for their ability to detect alterations in VWF levels following d ifferential processing of blood for testing, and specifically in (1) s erum compared to plasma and (2) filtered plasma compared to nonfiltere d plasma. Although all assays tended to detect some change, sensitivit y of detection varied between assays, with the VWF: CBA most consisten tly able to detect large decreases in VWF levels in serum and filtered plasma. The authors propose that the increased sensitivity of the VWF :CBA assay to VWF depleted in these circumstances is that this assay s electively detects higher molecular weight forms tie, those known to b e more functionally relevant), and that assay results reflect the pref erential incorporation of these forms in the platelet-fibrin-gel durin g the clotting process, and onto the filter matrix during filtration. To confirm this, multimer analysis was performed and showed a reductio n in high molecular weight forms of VWF in these cases. Finally, direc t evidence that the VWF:CBA assay preferentially detects high molecula r weight forms of VWF was obtained following fractionation of normal p lasma VWF (separation according to molecular weight using size exclusi on matrix; confirmed by specific multimer analysis) and assessment of eluted VWF, Using a standard VWF:Ag assay, detection of eluted VWF was unrelated to molecular size. In contrast, the VWF:CBA showed selectiv e detection, and was able to preferentially discriminate high and inte rmediate particular relevance to diagnostic pathology laboratories bec ause filtered plasma or serum can be inappropriately (and unknowingly) provided for the clinically queried diagnosis of von Willebrand's dis ease (VWD). As outlined in this report, these samples can yield VWF re sults that closely mimic those of a Type 2A or Type 2B VWD individual, and thus, VWD may be incorrectly diagnosed.