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Risk factors for subarachnoid haemorrhage

The process of systematic review is being applied in an ever-increasing number of fields. Bandolier was impressed by a systematic review of the risk factors for subarachnoid haemorrhage (SAH) from Utrecht [1].


Searches were done to find reports with the following criteria:-

  • SAH had to be recognised and analysed as a separate entity and not be included with a haemorrhagic stroke group.
  • Studies had to present crude data that could be recalculated in the analysis.
  • Case and control subjects had to be comparable, without additional criteria for controls.
  • For case-control studies the diagnosis of SAH had to be confirmed in over 70% of the cases by the presence of subarachnoid blood on CT or by demonstration of an aneurysm during angiography or autopsy.
  • For the longitudinal studies the diagnosis had to be based on a review of the medical records and not only on ICD codes.

Data were analysed on the basis of the following risk factors:-

  • Alcohol consumption (none, <150 g/week, >150 g/week)
  • Smoking (never smokers, former smokers, current smokers)
  • Hypertension
  • Hypercholesterolaemia
  • Oral contraceptive use
  • Hormone replacement use


There were nine longitudinal studies and 11 case-control studies which met the inclusion criteria. The figure shows results from more than one study.

Consistent increased risk was found for smoking, hypertension and alcohol intake of more than 150 grams/week (an average drink contains 12 grams of alcohol). Oral contraceptive use, hormone replacement therapy, and hypercholesterolaemia were not associated with an increased risk.

One study showed a possible protective effect of physical exercise with a relative risk of 0.5 (0.3 - 1.0), though the 95% confidence intervals just included 1.


The incidence of SAH is low, but about half of all patients who suffer SAH die due to the initial impact of the haemorrhage. Reducing deaths from SAH depends on reducing the risk for SAH in the population as a whole: those risks are the same as those for coronary artery disease, smoking, hypertension, lack of exercise and drinking too much.


  1. LL Teunissen, GJE Rinkel, A Algra, J van Gijn. Risk factors for subarachnoid hemorrhage: a systematic review. Stroke 1996 27: 544-9.

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