title: Clinical manifestations and anti-phospholipid antibodies in 712 patients with systemic lupus erythematosus: evaluation of two diagnostic assays.
abstract: OBJECTIVE
  To evaluate the agreement and performance of two tests for aPLs with regard to association with manifestations of the APS in patients with SLE.
  
  
  METHODS
  We investigated 712 SLE patients and 280 population controls. Cardiolipin and β(2) glycoprotein-I antibodies were measured with routine ELISA and a new automated method. Three positivity cut-offs (99%, 90% of controls and recommended cut-off by manufacturers) were used. Associations with previous thrombotic events, thrombocytopenia and, in a subgroup of patients, obstetric morbidity (n = 296) were evaluated. Results were compared with the LA test, performed in 380 patients.
  
  
  RESULTS
  Inter-test agreement was moderate (demonstrated by κ-values 0.16-0.71). Performance of the two tests was similar: at the 99th percentile cut-off, sensitivity for any thrombotic event ranged from 3.7% to 24.8%, while specificity was 84.7-97.7%. Regardless of assay, IgG isotypes were associated with venous thrombosis and ischaemic cerebrovascular disease, whereas aPLs of IgM isotype were weakly associated with ischaemic heart disease. Associations were greatly affected by aPL level. LA performed better than the specific aPL tests. LA was associated with any thrombotic event, odds ratio 5.4 (95% CI 3.1, 9.4), while the specific aPL tests ranged from non-significant to an odds ratio of 1.9 (95% CI 1.03, 3.4) using criteria cut-off. LA was also convincingly associated with other APS manifestations.
  
  
  CONCLUSIONS
  In relation to thrombotic manifestations, there was moderate agreement but no clear advantages when comparing a routine aPL ELISA with an automated method. APL isotype and titre as well as LA positivity are important for risk assessment in SLE patients.
authors.affiliation: Unit of Rheumatology, Department of Medicine Solna, Karolinska Institutet, Karolinska University Hospital,Stockholm, Sweden. anna.vikerfors@karolinska.se
authors.forename: Anna
authors.initials: A
authors.lastname: Vikerfors
authors.forename: Anna-Britta
authors.initials: AB
authors.lastname: Johansson
authors.forename: Johanna T
authors.initials: JT
authors.lastname: Gustafsson
authors.forename: Andreas
authors.initials: A
authors.lastname: Jönsen
authors.forename: Dag
authors.initials: D
authors.lastname: Leonard
authors.forename: Agneta
authors.initials: A
authors.lastname: Zickert
authors.forename: Gunnel
authors.initials: G
authors.lastname: Nordmark
authors.forename: Gunnar
authors.initials: G
authors.lastname: Sturfelt
authors.forename: Anders
authors.initials: A
authors.lastname: Bengtsson
authors.forename: Lars
authors.initials: L
authors.lastname: Rönnblom
authors.forename: Iva
authors.initials: I
authors.lastname: Gunnarsson
authors.forename: Kerstin
authors.initials: K
authors.lastname: Elvin
authors.forename: Elisabet
authors.initials: E
authors.lastname: Svenungsson
mesh_terms: D000328:Adult; D017153:Antibodies, Anticardiolipin / Q000032:analysis*; D016736:Antiphospholipid Syndrome / Q000175:diagnosis* / Q000503:physiopathology; D016022:Case-Control Studies; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D015200:Fluoroimmunoassay; D006801:Humans; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000032:analysis; D007075:Immunoglobulin M / Q000032:analysis; D016682:Lupus Coagulation Inhibitor / Q000032:analysis*; D008180:Lupus Erythematosus, Systemic / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012680:Sensitivity and Specificity; D053482:beta 2-Glycoprotein I / Q000276:immunology*
chemical_list: D017153:Antibodies, Anticardiolipin; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D016682:Lupus Coagulation Inhibitor; D053482:beta 2-Glycoprotein I