Laboratory testing for von Willebrand's disease: an assessment of current diagnostic practice and efficacy by means of a multi-laboratory survey

We report an evaluation of current laboratory practice for the diagnosis of von Willebrand's disease (VWD) by means of a multilaboratory survey. This assessment was undertaken with the RCPA Quality Assurance Program (QAP) in Haematology, which covers a wide geographic area encompassing Australia, Ne w Zealand and Asia. A total of 25 laboratories actively involved in testing for VWD were selected to participate in a sample testing assessment exerci se. Samples comprised 10 plasmas: (if a normal plasma pool tin duplicate), (ii) this pool diluted to 50% (in duplicate), (iii) a normal individual (XI ), (iv) severe Type I VWD (x1), (vf Type 2B VWD (x2 unrelated donors), (vi) Type 3 VWD tx I), (vii) Type 2A VWD (x1). Laboratories were asked to perfo rm all tests available to them in order to establish a laboratory diagnosis of VWD, and then to comment on the possibility or otherwise of VWD. Overal l findings indicated a wide variation in test practice, in the effectivenes s of various test procedures in detecting: VWD, and in the ability of vario us composite test panels to identify type 2 VWD subtypes. Firstly, while al l laboratories (n = 25) performed tests For FVIII:C activity, von Willebran d factor 'antigen' (VWF:Ag) and a functional VWF assay [using the ristoceti n cofactor assay (VWF:RCo; n = 23) and/or the collagen binding assay (VWF:C BA; n = 12)], only three laboratories carried out VWF:Multimer analysis. Se condly, for the three quantitative VWF assays, 10/25 (40%) laboratories per formed all three, whereas 15/25 (60%) performed only two [VWF:Ag and VWF:RC o (n = 13); VWF:AI: and VWF:CBA (n = 2)]. Thirdly, a variety of assay metho dologies were evident for VWF:Ag [ELISA, electro-immuno diffusion (EID), la tex immune-assay (LIA), and VIDAS assay] and VWF:RCo (platelet agglutinatio n/'aggregometry' and a 'functional VWF:RCo-alternative' ELISA assay). Betwe en method analysis for the quantitative VWF assays showed that the VWF:RCo yielded the greatest degree of inter-laboratory assay variation, and had th e poorest overall performance with respect to sensitivity to low levels of VWF. The VWF:CBA also performed better than the VWF:RCo in terms of ability to detect functional VWF 'discordance' (i.e. Type 2 VWD). Within VWF:AE: m ethod analysis showed that the EID assay procedure was associated with the greatest variation in assay results, while the EID and LIA test methods sho wed poorer sensitivity at low VWF levels compared to the ELISA method. With in the VWF:RCo assay procedure, greatest variation in assay results and poo rest sensitivity to low VWF levels was obtained using the agglutination met hod; however, the agglutination procedure showed better performance than th e 'functional VWF:RCo-alternative' ELISA assay in identifying Type 2 VWD pl asma samples. Finally, despite identified variations,most laboratories appe ared to understand the complexities involved in the VWD-diagnostic process, and made appropriate diagnostic predictions regarding tested samples. From a total possible 246 interpretation events, laboratories in most cases cor rectly identified normal samples as normal (67/75 events = 89%), and VWD sa mples as derived from individuals with VWD (117/121 events = 97%). Moreover , when VWD was suggested by laboratory findings, laboratories usually corre ctly predicted the general subtype of VWD present (96/109 events = 88%). Wh en 'misinterpretations' occurred, these could often be linked to the test p anels utilised by laboratories. That is, laboratories using the VWF:AE. and VWF:RCo combination were more likely to incorrectly identify samples de rived from Type 2 VWD patients as being Type 1,Type 1 VWD patients as being Type 2, and normal plasma samples as potentially derived from patients wit h VWD, compared to those using the VWF:Ag and VWF:CBA.