The Ottawa SAH Rule

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.
JAMA. 2013;310(12):1248-1255.

Newman-Toker DE, Edlow JA.
High-stakes diagnostic decision rules for serious disorders: the Ottawa subarachnoid hemorrhage rule.
JAMA. 2013;310(12):1237-1239.

Neurology Reviews. 2013 21(11):6-8.