title: Real world experience with antiphospholipid antibody tests: how stable are results over time?
abstract: OBJECTIVE
  To determine the stability and the degree of variation of antiphospholipid antibody (aPL) results over time in a large cohort of well evaluated aPL positive patients; and to analyse factors contributing to aPL variation and the validity of aPL in a real world setting in which aPL tests are done in multiple laboratories.
  
  
  METHODS
  The clinical characteristics, drug treatment, and 1652 data points for lupus anticoagulant (LA), anticardiolipin antibodies (aCL), and anti-beta2 glycoprotein I antibodies (anti-beta2GPI) were examined in 204 aPL positive patients; 81 of these met the Sapporo criteria for antiphospholipid syndrome (APS) and 123 were asymptomatic bearers of aPL.
  
  
  RESULTS
  87% of initially positive LA results, 88% of initially negative to low positive aCL results, 75% of initially moderate to high positive aCL results, 96% of initially negative to low positive anti-beta2GPI results, and 76% of initially moderate to high positive anti-beta2GPI results subsequently remained in the same range regardless of the laboratory performing the test. Aspirin, warfarin, and hydroxychloroquine use did not differ among patients whose aCL titres significantly decreased or increased or remained stable. On same day specimens, the consistency of aCL results among suppliers ranged from 64% to 88% and the correlation ranged from 0.5 to 0.8. Agreement was moderate for aCL IgG and aCL IgM; however, for aCL IgA agreement was marginal.
  
  
  CONCLUSIONS
  aPL results remained stable for at least three quarters of subsequent tests, regardless of the laboratory performing the test; the small amount of variation that occurred did not appear to be caused by aspirin, warfarin, or hydroxychloroquine use.
authors.affiliation: Department of Rheumatology, Hospital for Special Surgery, Weill Medical College of Cornell University, 535 E70th Street, New York, NY 10021, USA. derkan@pol.net
authors.forename: D
authors.initials: D
authors.lastname: Erkan
authors.forename: W J M
authors.initials: WJ
authors.lastname: Derksen
authors.forename: V
authors.initials: V
authors.lastname: Kaplan
authors.forename: L
authors.initials: L
authors.lastname: Sammaritano
authors.forename: S S
authors.initials: SS
authors.lastname: Pierangeli
authors.forename: R
authors.initials: R
authors.lastname: Roubey
authors.forename: M D
authors.initials: MD
authors.lastname: Lockshin
mesh_terms: D000328:Adult; D017153:Antibodies, Anticardiolipin / Q000097:blood; D017152:Antibodies, Antiphospholipid / Q000097:blood*; D016736:Antiphospholipid Syndrome / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D015331:Cohort Studies; D005260:Female; D006023:Glycoproteins / Q000276:immunology; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000097:blood; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D053482:beta 2-Glycoprotein I
chemical_list: D017153:Antibodies, Anticardiolipin; D017152:Antibodies, Antiphospholipid; D015415:Biomarkers; D006023:Glycoproteins; D016682:Lupus Coagulation Inhibitor; D053482:beta 2-Glycoprotein I
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