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 loss 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.