title: Cooperation experience in a multicentre study to define the upper limits in a normal population for the diagnostic assessment of the functional lupus anticoagulant assays.
abstract: BACKGROUND
  Phospholipid-dependent coagulation tests for lupus anticoagulant (LA) are considered an important step for the diagnosis of anti-phospholipid syndrome; however, LA laboratory detection is difficult because of many variables. Five hospital laboratories, located in a North-Italy area and using the same method for LA testing, cooperated to standardise sample treatment and analytical procedure in order to define the upper values for LA negativity.
  
  
  METHODS
  In total, 200 normal subjects (40 for each centre) were studied for six LA functional assays, using the same procedure, reagent lot and analyser type. The first tests done were LA screen and LA confirm assays, based on diluted Russell's Viper Venom Time, with low and high phospholipid content, respectively. The second tests performed were silica clotting time screen and confirm assays, based on activated partial thromboplastin time, with low and high phospholipid content, respectively. Finally, two mixing assays were executed for both screening assays, diluting patient sample with a pool prepared with plasma collected from the study population.
  
  
  RESULTS
  Data analysis demonstrated a difference between centres for all assays when results were expressed in seconds; the difference disappeared when results are normalised with the local mean normal value of each centre and are expressed as a normalised ratio. The study population was normally distributed; so the value corresponding to 99th percentile was used as limit value for LA negativity. Values expressed as normalised ratio, for LA and silica clotting time screenings were 1.22 and 1.23, respectively.
  
  
  CONCLUSIONS
  The study allowed us to define a uniform approach to LA testing and evaluation for laboratories employing the same methods.
authors.affiliation: Haemostasis Laboratory, Department of Transfusion Medicine, AOUTs Ospedali riuniti, University Hospital of Cattinara, Strada di Fiume 447, 34149 Trieste, Italy. paola.pradella@aots.sanita.fvg.it
authors.forename: Paola
authors.initials: P
authors.lastname: Pradella
authors.forename: Gabriella
authors.initials: G
authors.lastname: Azzarini
authors.forename: Liliana
authors.initials: L
authors.lastname: Santarossa
authors.forename: Livio
authors.initials: L
authors.lastname: Caberlotto
authors.forename: Cristina
authors.initials: C
authors.lastname: Bardin
authors.forename: Alessandra
authors.initials: A
authors.lastname: Poz
authors.forename: Federica
authors.initials: F
authors.lastname: D'Aurizio
authors.forename: Roberta
authors.initials: R
authors.lastname: Giacomello
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016736:Antiphospholipid Syndrome / Q000097:blood* / Q000175:diagnosis* / Q000276:immunology; D001780:Blood Coagulation Tests / Q000592:standards*; D005260:Female; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000097:blood*; D008297:Male; D008875:Middle Aged; D015337:Multicenter Studies as Topic; D012016:Reference Values; D055815:Young Adult
chemical_list: D016682:Lupus Coagulation Inhibitor