title: Performance and clinical utility of a commercial von Willebrand factor collagen binding assay for laboratory diagnosis of von Willebrand disease.
abstract: BACKGROUND
  Von Willebrand disease (VWD) diagnosis and classification usually require a combination of nonspecific and VW-factor (VWF)-specific assays. We evaluated the analytical performance of a commercially available collagen-binding assay (CBA) and its usefulness in conjunction with other assays for laboratory diagnosis of VWD.
  
  
  METHODS
  We used a commercial CBA ELISA (Life Technologies) to evaluate 3085 plasma samples. We used standard procedures to perform other assays, including factor VIII activity (FVIII:C), VWF antigen (VWF:Ag), ristocetin cofactor activity, VWF collagen binding capacity (VWF:CB), and VWF multimeric analysis.
  
  
  RESULTS
  CBA intra- and interassay CVs were <6% and <13%, respectively. Reference intervals were 45%-198% for VWF:CB and 0.75-1.32 for the VWF:CB/Ag ratio. Of 3085 samples tested, 235 (8%) had results commonly associated with VWD. Multimer analysis and phenotypic data in 156 samples identified VWD types as: 91 (58%) type 1, 62 (40%) type 2, and 3 (2%) type 3. Of the 91 type 1 samples, proportional decreases in functional activity were seen in 75 samples (82%) according to CBA and in 63 samples (69%) according to the ristocetin cofactor assay. Of the type 2 samples, 10 were further identified as probable type 2A, 26 as probable type 2B, 12 as probable type 2M, and 14 could not be subtyped. VWF:CBA/Ag ratios <0.5 occurred in 83% of VWD type 2A and 2B samples, indicating characteristic functional discordance. Mean (SD) VWF:CB values were significantly higher in individuals without group O blood [113 (45)] than in those with group O blood [83 (32)] (t-test, P = 0.007).
  
  
  CONCLUSIONS
  The commercial CBA assay produces reliable results and is useful for laboratory diagnosis of VWD.
authors.affiliation: Coagulation Department, Quest Diagnostics Nichols Institute, San Juan Capistrano, CA 92690, USA. joanna.m.popov@questdiagnostics.com
authors.forename: Joanna
authors.initials: J
authors.lastname: Popov
authors.forename: Olga
authors.initials: O
authors.lastname: Zhukov
authors.forename: Susan
authors.initials: S
authors.lastname: Ruden
authors.forename: Terry
authors.initials: T
authors.lastname: Zeschmann
authors.forename: Anthony
authors.initials: A
authors.lastname: Sferruzza
authors.forename: Mervyn
authors.initials: M
authors.lastname: Sahud
mesh_terms: D003094:Collagen / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D010641:Phenotype; D011485:Protein Binding; D012016:Reference Values; D015203:Reproducibility of Results; D014842:von Willebrand Diseases / Q000175:diagnosis*; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D014841:von Willebrand Factor; D003094:Collagen