Clinical significance of anti-protein Z antibodies in patients with lupus anticoagulant

Introduction: 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). Materials and 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 toss than in those with normal pregnancy, but the difference was not statistically significant. Conclusion: 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. (C) 2007 Elsevier Ltd. All rights reserved.