Risk factors for subarachnoid hemorrhage: a systematic review

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.

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.

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, 2.9 to 4.3); (2) hypertension (RR, 2.8; 95% CI, 2.1 to 3.6; OR, 2.9; 95% CI, 2.4 to 3.7) and (3) drinking 150 g or more of alcohol per week (RR, 4.7; 95% CI, 2.1 to 10.5; OR, 1.5; 95% CI, 1.1 to 1.9). Use of oral contraceptives, hormone replacement therapy, hypercholesterolemia, and physical activity were not significantly related to the risk of SAH.

We conclude that smoking, hypertension, and alcohol abuse are important risk factors for SAH. Reduction of exposure to these risk factors might result in a decreased incidence of SAH.