Protein Z in ischaemic stroke

Many risk factors associated with ischaemic stroke are known, including high levels of fibrinogen or factor VII. Protein Z is a vitamin K‐dependent coagulation factor, which was found to promote the assembly of thrombin with phospholipid vesicles that might promote coagulation. Indeed, a low protein Z level may be associated with a varying bleeding tendency. Therefore, we hypothesized that high protein Z levels could induce a hypercoagulable state and performed a case–control study to investigate a potential association between high protein Z plasma levels and ischaemic stroke. We measured protein Z in plasma samples from 157 patients with stroke of unknown aetiology and 192 control subjects. All patients had survived an ischaemic stroke or transient ischaemic attack (TIA) for at least 2 months. We found an increased relative risk of ischaemic stroke with increasing protein Z levels, with an odds ratio of 4·3 [95% confidence interval (CI): 1·7–11] for protein Z plasma levels ≥ 160%. Excluding patients with a history of venous thromboembolism from the analysis, the same result was obtained (odds ratio 4·2; 95% CI: 1·6–11·2). Using a logistic regression model, this association also remained significant (P = 0·04) after adjustment for established risk factors. Our data indicated that a high plasma level of protein Z is an independent risk factor for ischaemic stroke.