Written by Shannon Markus
Spoon Feed
Both the Ottawa and Emerald Subarachnoid Hemorrhage (SAH) Rules are highly sensitive for excluding SAH in ED patients with non-traumatic acute headaches presenting to the emergency department but have low specificity. Importantly, rule implementation did not significantly reduce CT scan utilization.
So you’re saying there’s a chance of SAH
This systematic review and meta-analysis evaluates the diagnostic accuracy and clinical impact of the Ottawa and Emerald SAH Rules in emergency department (ED) patients with acute non-traumatic headache. Across 12 included studies (10,338 patients for Ottawa; 2,550 for Emerald), both rules demonstrated high pooled sensitivity (99%) and low negative likelihood ratios, making them pretty good at ruling out non-traumatic SAH when negative. However, specificity was low (23% for Ottawa, 27% for Emerald), indicating that many patients without SAH would still undergo imaging (read: very limited effectiveness in reducing unnecessary imaging). Meta-analysis revealed no significant decrease in CT utilization following Ottawa rule implementation (OR 1.15; 95% CI: 0.62–2.13) and there wasn’t enough data to determine this for the Emerald Rule. Subgroup analyses revealed heterogeneity related to study design, population characteristics, and setting, limiting the strength of the study. Despite impressive sensitivity, the rules have limited impact on imaging rates and still need further external validation.
How does this change my practice?
While I think the results are interesting, I’m not sure it will change my practice much. Application of the rules would make me more confident in decisions to forego scans when negative, but based on this group of studies, we as emergency physicians might already be pretty good at weeding those patients out based on clinical gestalt alone.
Editor’s Note: The authors state that patients with any positive finding in the Ottawa rule should get a CT. I patently disagree with this and would urge use of the Ottawa SAH tool only as a one-way rule (if at all), like PERC. ~Nick Zelt
Source
Diagnostic Accuracy and Application of Subarachnoid Hemorrhage Decision Rules Among Patients With Non-Traumatic Acute Headache: A Systematic Review and Meta-Analysis. Acad Emerg Med. 2025 Jul 2. doi: 10.1111/acem.70087. Epub ahead of print. PMID: 40605232
