Risk factors for subarachnoid hemorrhage.

Background and Purpose Knowledge of modifiable risk factors for subarachnoid hemorrhage (SAH) is important in terms of prevention. We therefore conducted a systematic review of studies on risk factors for SAH, with emphasis on sufficiently precise criteria for the diagnosis of SAH. Methods To identify studies we performed a Medline search from 1966 to 1994 and searched the reference lists of all relevant publications. Studies were included only if they fulfilled predefined methodological criteria. Case-control studies were included if the diagnosis of SAH was proved by CT, angiography, or autopsy in at least 70% of patients. Longitudinal studies were included if the criteria for SAH were based on a review of the medical records. Results Nine longitudinal studies and 11 case-control studies were included. Significant risk factors were as follows: (1) smoking (relative risk [RR] for longitudinal studies, 1.9; 95% confidence interval [CI], 1.5 to 2.3; odds ratio [OR] for case-control studies, 3.5; 95% CI, 2....