Inclusion Criteria:  age ≥ 18 years hospital admission due to an aneurysmal subarachnoid hemorrhage (diagnosis radiologically confirmed)  Exclusion Criteria:  non-aneurysmal subarachnoid hemorrhage (eg. trauma, perimesencephalic subarachnoid hemorrhage). participation in another study with CSF sampling or an interventional medical product within the 30 days preceding and during the present study. previous enrolment into the current study