title: Type 2M von Willebrand disease - more often misidentified than correctly identified.
abstract: BACKGROUND
  Appropriate diagnosis of von Willebrand disease (VWD), including differential identification of qualitative vs. quantitative von Willebrand factor (VWF) defects has important management implications, but remains problematic.
  
  
  OBJECTIVE
  The aim of the study was to assess whether 2M VWD, defining qualitative defects not associated with loss of high molecular weight (HMW) VWF, is often misidentified, given highly variable reported frequency ranging from 0 to ~60% of all type 2 VWD.
  
  
  METHODS
  A comparative evaluation of laboratory ability to appropriately identify 2M VWD (n = 4) vs. HMW VWF reduction (n = 4), as sent to participants of an international external quality assessment programme.
  
  
  RESULTS
  Laboratories had considerably greater difficulty identifying type 2M VWD, correctly identifying these on average only 29.4% of occasions, with the 70.6% error rate representing use of insufficient test panels (41.7%), misinterpretation of test results (10.0%) and analytical errors (13.3%). One type 2M case, giving a median of 49 U dL(-1) VWF:Ag, was more often misidentified as type 2A/2B VWD (46.7%) than 2M (34.8%). Another 2M case, giving a median of 189 U dL(-1) VWF:Ag, was instead often misidentified as being normal (non-VWD) (36.4%), with identifications of type 2A/2B VWD (13.6%) also represented. In comparison, errors in identification of HMW VWF reduced samples only averaged 11.5%, primarily driven by use of insufficient test panels (6.3%) or misinterpretation of results (4.2%) and infrequently analytical errors (1.0%).
  
  
  CONCLUSIONS
  Type 2M VWD is more often misidentified (70.6%) than correctly identified as 2M VWD (29.4%), and potentially explaining the relative under-reported incidence of 2M VWD in the literature.
authors.affiliation: Department of Haematology, Sydney Centres for Thrombosis and Haemostasis, Institute of Clinical Pathology and Medical Research (ICPMR), Pathology West, NSW Health Pathology, Westmead Hospital, Westmead, NSW, Australia.
authors.forename: E J
authors.initials: EJ
authors.lastname: Favaloro
authors.affiliation: RCPAQAP Haematology, St Leonards, NSW, Australia.
authors.forename: R A
authors.initials: RA
authors.lastname: Bonar
authors.affiliation: Department of Haematology, Sydney Centres for Thrombosis and Haemostasis, Institute of Clinical Pathology and Medical Research (ICPMR), Pathology West, NSW Health Pathology, Westmead Hospital, Westmead, NSW, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Mohammed
authors.affiliation: Mater Pathology, Mater Health Services, Brisbane, Qld, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Arbelaez
authors.affiliation: Mater Pathology, Mater Health Services, Brisbane, Qld, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Niemann
authors.affiliation: Mater Pathology, Mater Health Services, Brisbane, Qld, Australia.
authors.forename: R
authors.initials: R
authors.lastname: Freney
authors.affiliation: Department of Haematology and Cell Biology, Faculty of Health Sciences, University of the Free State, Bloemfontein, South Africa.
authors.forename: M
authors.initials: M
authors.lastname: Meiring
authors.affiliation: RCPAQAP Haematology, St Leonards, NSW, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Sioufi
authors.affiliation: RCPAQAP Haematology, St Leonards, NSW, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Marsden
mesh_terms: D001315:Australia; D001777:Blood Coagulation / Q000235:genetics; D001792:Blood Platelets / Q000502:physiology; D001798:Blood Proteins / Q000032:analysis* / Q000737:chemistry / Q000235:genetics; D019411:Clinical Laboratory Techniques / Q000592:standards; D003937:Diagnosis, Differential; D003951:Diagnostic Errors / Q000517:prevention & control / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D009154:Mutation / Q000235:genetics; D009520:New Zealand; D012016:Reference Values; D056728:von Willebrand Disease, Type 2 / Q000175:diagnosis* / Q000453:epidemiology; D014841:von Willebrand Factor / Q000032:analysis* / Q000737:chemistry / Q000235:genetics
chemical_list: D001798:Blood Proteins; D014841:von Willebrand Factor
keywords: 2M VWD; diagnosic; errors; interpretation; laboratory testing; von Willebrand disease; von Willebrand factor