title: Standardization of lupus anticoagulant. Feasibility study of a calibration model to minimize between-method variability.
abstract: BACKGROUND
  Results for lupus anticoagulant (LA) are currently expressed as ratio of patient-to-normal clotting times (LA-ratio). Yet, numerical results do vary according to the method used for testing, thus making difficult the between-method comparison of results. We hypothesized that the standardization model currently used for the INR for patients on oral-anticoagulants (OAT) would be of value also for LA standardization.
  
  
  METHODS
  To test this hypothesis we determined a sensitivity index valid for LA (called LASI) for six LA-detection methods against a common-standard using two sets of calibration-plasmas: (i)normal-plasmas spiked with IgG derived from patients strongly-positive for LA or (ii)plasmas from LA-positive patients. The LASI was then used to convert the LA-ratio into the standardized-LA-ratio (SLA-ratio) according to the equation: SLA-ratio = (LA-ratio)(LASI).
  
  
  RESULTS
  We demonstrate that (i)the model is feasible because calibration plots of log-transformed clotting times obtained for the LA-detection methods-vs.-the common-standard gave acceptable LASI values; (ii)the model is effective because between-method variability expressed as coefficient of variation, which was 42.8% with results expressed as LA-ratio, decreased to 7.8% with results expressed as SLA-ratio; (iii)the LASI value calculated with the LA-positive plasmas is more effective in minimizing between-method variability than the LASI value calculated with IgG-spiked plasmas.
  
  
  CONCLUSIONS
  A model of LA calibration similar to the INR for patients on OAT is feasible by using plasmas from LA-positive patients instead of patients on OAT. Potential application of the model are:(i)to compare the relative responsiveness of different LA-detection methods,(ii)to minimize differences between their results and (iii)to quantify LA potency.
authors.affiliation: Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, Department of Internal Medicine, Milano, Italy. armando.tripodi@unimi.it
authors.forename: Armando
authors.initials: A
authors.lastname: Tripodi
authors.forename: Veena
authors.initials: V
authors.lastname: Chantarangkul
authors.forename: Marigrazia
authors.initials: M
authors.lastname: Clerici
authors.forename: Claudia
authors.initials: C
authors.lastname: Palmucci
authors.forename: Elisa
authors.initials: E
authors.lastname: Bison
authors.forename: Alessandra
authors.initials: A
authors.lastname: Banzato
authors.forename: Eugenia
authors.initials: E
authors.lastname: Biguzzi
authors.forename: Vittorio
authors.initials: V
authors.lastname: Pengo
mesh_terms: D001780:Blood Coagulation Tests / Q000592:standards*; D002138:Calibration; D005240:Feasibility Studies; D006801:Humans; D019934:International Normalized Ratio / Q000592:standards; D016682:Lupus Coagulation Inhibitor / Q000627:therapeutic use*; D012015:Reference Standards; D015203:Reproducibility of Results
chemical_list: D016682:Lupus Coagulation Inhibitor