C5 and subarachnoid hemorrhage: aSAH patients with a high burden of subarachnoid hemorrhage were found to have the highest thrombin levels.18 We would expect that patients with CSF samples from a ventricular drain would have an increased amount of subarachnoid blood on the initial scan compared to patients with lumbar CSF samples, which in turn would result in increased C5a levels in CSF and thus higher levels of thrombin and C5a in the eculizumab group.