title: Clinical significance of anti-protein Z antibodies in patients with lupus anticoagulant.
abstract: BACKGROUND
  Protein Z serves as cofactor for the inactivation of factor Xa by the plasma protein Z-dependent protease inhibitor. Deficiency of protein Z was reported to exhibit a clinical manifestation like lupus anticoagulant characterised by thrombosis and fetal loss. As anti-protein Z antibodies may be associated with low protein Z levels, we hypothesised that anti-protein Z antibodies might play a role in lupus anticoagulant (LA).
  
  
  METHODS
  Anti-protein Z antibodies were measured by commercially available ELISA in 102 LA-patients (69 with and 33 without thrombosis) and 33 healthy volunteers.
  
  
  RESULTS
  Elevated anti-protein Z IgG and/or IgM, IgG and IgM antibody levels were more prevalent among LA-patients (62%, 35%, 45%) than among controls (50%, 25%, 25%), but the difference was only statistically significant for the IgM subtype (p=0.037). Anti-protein Z IgG (odds ratio [OR] 0.77, 95% confidence interval [CI] 0.33-1.82) and IgM (OR 0.82, CI 0.35-1.88) antibody levels in the highest quartile of controls did not indicate an increased risk for thrombosis among LA-patients. Anti-protein Z IgG (OR 2.0, CI 0.5-7.6) and IgM (OR 1.8, CI 0.5-6.6) antibody levels in the highest quartile of controls were more prevalent in women with pregnancy loss than in those with normal pregnancy, but the difference was not statistically significant.
  
  
  CONCLUSIONS
  Our data indicate that anti-protein Z antibodies are not associated with thrombosis in LA. However, women with LA and pregnancy loss show a tendency towards elevated anti-protein Z antibody levels.
authors.affiliation: Department of Internal Medicine I, Division of Hematology and Hemostaseology, Medical University of Vienna, Waehringer Gürtel 18-20, A-1090 Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Sailer
authors.forename: Rainer
authors.initials: R
authors.lastname: Vormittag
authors.forename: Silvia
authors.initials: S
authors.lastname: Koder
authors.forename: Peter
authors.initials: P
authors.lastname: Quehenberger
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kaider
authors.forename: Ingrid
authors.initials: I
authors.lastname: Pabinger
mesh_terms: D000022:Abortion, Spontaneous; D000328:Adult; D000368:Aged; D001798:Blood Proteins / Q000737:chemistry*; D015331:Cohort Studies; D015951:Factor Xa / Q000737:chemistry*; D005260:Female; D006487:Hemostasis; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D011248:Pregnancy Complications; D012008:Recurrence
chemical_list: D001798:Blood Proteins; D016682:Lupus Coagulation Inhibitor; C026080:plasma protein Z; D015951:Factor Xa