title: Modified phosphatidylserine-dependent antiprothrombin [corrected] ELISA enables identification of patients negative for other antiphospholipid antibodies and also detects low avidity antibodies.
abstract: BACKGROUND
  Two approaches for detecting anti-prothrombin antibodies have been described. The first detects antibodies against prothrombin alone and the second, phos-phatidylserine-dependent antiprothrombin antibodies. The latter more often correlate with clinical manifestations of antiphospholipid syndrome and with lupus anticoagulant activity.
  
  
  METHODS
  In order to increase the capacity of antibody binding, we modified the previously described phosphatidylser-ine-dependent antiprothrombin ELISA and determined their avidity. We examined 203 patients with systemic autoimmune diseases and 222 blood donors.
  
  
  RESULTS
  Our modification resulted in a greater intensity of antibody binding to prothrombin on phosphatidylserine-coated plate surfaces compared to the previously described method. By changing ELISA conditions, we were able to detect with one assay the two, presumably different, populations of antiprothrombin antibodies. Diagnostic specificities of both ELISAs for antiphospholipid syndrome were similar (92.5% vs. 93.1%), while the sensitivity of the modified phosphatidylserine-dependent antiprothrombin ELISA was significantly higher than the anti-prothrombin alone ELISA (59% vs. 25%). Low avidity antiprothrombin antibodies were only detected in the modified phosphatidylserine-dependent antiprothrombin ELISA. Four percent of patients with positive phosphatidylserine-dependent antiprothrombin antibodies, showing clinical manifestations of antiphospholipid syndrome, were negative for all other antiphospholipid antibodies. The risk for antiphospholipid syndrome increased with the number of antiphospholipid antibody positivity.
  
  
  CONCLUSIONS
  We conclude that antibodies detected with a modified phosphatidylserine-dependent antiprothrombin ELISA could improve the diagnosis of antiphospholipid syndrome by offering additional information on the risk for thrombosis, especially in patients negative for other antiphospholipid antibodies.
authors.affiliation: Immunology Laboratory, Department of Rheumatology, University Medical Centre, Ljubljana, Slovenia. polona.zigon@guest.arnes.si
authors.forename: Polona
authors.initials: P
authors.lastname: Žigon
authors.forename: Aleš
authors.initials: A
authors.lastname: Ambrožič
authors.forename: Saša
authors.initials: S
authors.lastname: Čučnik
authors.forename: Tanja
authors.initials: T
authors.lastname: Kveder
authors.forename: Blaž
authors.initials: B
authors.lastname: Rozman
authors.forename: Borut
authors.initials: B
authors.lastname: Božič
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D017152:Antibodies, Antiphospholipid / Q000032:analysis* / Q000276:immunology; D000915:Antibody Affinity; D000991:Antithrombins / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010718:Phosphatidylserines / Q000378:metabolism*; D011516:Prothrombin / Q000276:immunology; D055815:Young Adult
chemical_list: D017152:Antibodies, Antiphospholipid; D000991:Antithrombins; D010718:Phosphatidylserines; D011516:Prothrombin