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Ottawa SAH Rule

Identifies which alert patients with acute non-traumatic headache need investigation for subarachnoid hemorrhage — any single positive criterion means investigate.

SAH ruled out clinically
No Ottawa SAH Rule criteria present · 100% sensitivity (95% CI 97.2–100%)
Return precautions: worsening headache, new neck stiffness, fever, neurologic symptoms
0pts
Age ≥40 years
Neck pain or stiffness
Witnessed loss of consciousness
Onset during exertion
Thunderclap headache (instantly peaking)
Limited neck flexion on examination
Applies only to alert (GCS 15) patients ≥15 years with a new, non-traumatic headache peaking within 1 hour. Does NOT apply with focal deficits, papilledema, recurrent similar headaches, or known aneurysm/SAH. A negative CT does not clear SAH beyond ~6 hours — sensitivity falls from ~98% at 6h to ~86% by 72h.