For alert patients older than 15 y with new severe nontraumatic headache reaching maximum intensity within 1 h
Not for patients with new neurologic deficits, previous aneurysms, SAH, brain tumors, or history of recurrent headaches (>=3 episodes over the course of >=6 mo)
Investigate if >=1 high-risk variables present:
1. Age >=40 y
2. Neck pain or stiffness
3. Witnessed loss of consciousness
4. Onset during exertion
5. Thunderclap headache (instantly peaking pain)
6. Limited neck flexion on examination
Overall sensitivity of 99.2% and a specificity of 99.6% in identifying SAHs
Perry JJ, Stiell IG, Sivilotti ML, et al.
Clinical decision rules to rule out subarachnoid hemorrhage for acute headache.
Newman-Toker DE, Edlow JA.
High-stakes diagnostic decision rules for serious disorders: the Ottawa subarachnoid hemorrhage rule.
Richard Pearson 2014