title: Screening for lupus anticoagulant: improving the performance of the lupus-sensitive PTT-LA.
abstract: BACKGROUND
  The aim of the present work was to verify whether calculating a ratio between clotting times obtained with the sensitive PTT-LA and a less sensitive activated partial thromboplastin time (aPTT)-reagent may represent a valuable aPTT-based screening strategy for lupus anticoagulants (LA).
  
  
  METHODS
  For the pilot study, plasma samples from normal subjects (n = 15) and from patients with LA (n = 10), therapeutic anticoagulation with vitamin K-antagonists (VKA) (n = 15) or unfractionated heparin (n = 15), coagulation factors deficiency (n = 16), and inhibitory antibodies against factor VIII or IX (n = 11) were studied. For the evaluation study, 1553 consecutive plasma samples from nonanticoagulated patients investigated for LA between January 2005 and December 2007 at our institution were studied. Following screening strategies were employed: Pathromtin-SL (aPTT-SL), PTT-LA (aPTT-LA), ratio aPTT-LA/aPTT-SL (aPTT-ratio), and Russell's viper venom (RVV) based LA-Check. LA positive samples were identified by mixing studies and diluted RVV confirmation test (LA-Check/LA-Sure).
  
  
  RESULTS
  Pilot study: All screening strategies had a 100% sensitivity, and the aPTT-ratio reached the highest specificity (82%; 95%CI: 74-90%). Within the evaluation study, following sensitivities for LA screening were observed: aPTT-SL 59.0% (95%CI: 57-61%), aPTT-LA 82.1% (95%CI: 80-84%), aPTT-ratio 92.3% (95%CI: 91-94), and LA-Check 83.3% (95%CI: 82-85%).
  
  
  CONCLUSIONS
  Calculating a ratio between the LA-sensitive PTT-LA and the less sensitive Pathromtin-SL improves the performance of the PTT-LA itself and represents a simple and sensitive aPTT-based integrated strategy for LA screening.
authors.affiliation: Department of Haematology, Central Haematology Laboratory, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Luginbühl
authors.forename: G
authors.initials: G
authors.lastname: Barizzi
authors.forename: I
authors.initials: I
authors.lastname: Sulzer
authors.forename: B
authors.initials: B
authors.lastname: Lämmle
authors.forename: L
authors.initials: L
authors.lastname: Alberio
mesh_terms: D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000097:blood*; D008403:Mass Screening / Q000379:methods*; D010314:Partial Thromboplastin Time / Q000592:standards*; D010865:Pilot Projects; D012016:Reference Values; D012680:Sensitivity and Specificity
chemical_list: D016682:Lupus Coagulation Inhibitor