Assessment of current diagnostic practice and efficacy in testing for von Willebrand's disorder: results from the...

This study reports an evaluation of current laboratory practice for the diagnosis of von Willebrand's disorder (VWD) by means of a multi-laboratory (n = 19) survey (the 'Second Australasian VWD Survey'). Results are compared with a previously conducted but similarly comprehensive survey ('Survey-1'). Samples comprised a new set of seven plasmas: (i) Type 3 VWD; (ii) Type 2B VWD; (iii) Moderate Type 1 VWD/Haemophilia A combined defect; (iv) Normal individual; (v) Mild Type 1 VWD; (vi) Type 2M/2A VWD; (vii) Type 2N VWD. Overall, many current findings confirmed those reported in Survey-1 [including between-method analysis, within-method analysis, inter-laboratory assay variation, sensitivity to low levels of von Willebrand Factor (vWF), detection of functional vWF 'discordance', and appropriateness of diagnostic predictions]. Novel findings include: (i) although vWF:collagen binding activity (vWF:CBA) performed better than vWF:ristocetin cofactor (vWF:RCof) assay in identification of functional discordance in Type 2B VWD, both assays performed equally in identification of discordance in the Type 2M/2A VWD; (ii) most laboratories failed to identify the Type 2N VWD as a potential 2N utilizing vWF antigen (vWF:Ag) and factor VIII coagulant (FVIII:C) testing as a screening process; (iii) this particular survey was followed up by a dry workshop attended by over 45 scientists from Australia and New Zealand, and comprising representatives from most survey participants. Discussion covered many topics including the effect of blood group, the role (if any) of the bleeding time, the role of the PFA-100, confirmatory and additional tests, and the possibility of restricting testing to specialized centres. Consensus was reached on the following points: (i) diagnosis of VWD requires both clinical and laboratory assessment; (ii) testing should comprise FVIII:C, vWF:Ag and either/or both vWF:RCof and vWF:CBA; (iii) laboratory results should be reviewed in the light of clinical findings; and (iv) confirmatory repeat testing should be performed on a sample taken 6 weeks later.