More than 150,000 people visit Canadian emergency departments each year because of acute headache. While it usually isn’t serious, in 1-3 percent of cases a bad headache can be a sign of dangerous bleeding in the brain, also called subarachnoid hemorrhage or SAH.

Dr. Jeffrey Perry and his colleagues developed the Ottawa Subarachnoid Hemorrhage Rule to help emergency doctors determine which headache patients might have SAH. A new study published in CMAJ journal validates the rule in more than a thousand patients in six hospitals, showing that it could detect 100% of SAH cases. A previous analysis estimated this would save 25 lives each year in Ontario. The rule also allowed doctors to rule out SAH in 13% of headache patients without the need for brain imaging.

The authors defined subarachnoid hemorrhage as detection of any of the following: subarachnoid blood visible upon computed tomography of the head (from the final report by the local radiologist); xanthochromia in the cerebrospinal fluid (by visual inspection); or the presence of erythrocytes (> 1 × 106/L) in the final tube of cerebrospinal fluid, with an aneurysm or arteriovenous malformation visible upon cerebral angiography.

Researchers at The Ottawa Hospital and the University of Ottawa are internationally recognized for their clinical decision rules.