Rule out subarachnoid haemorrhage in acute non-traumatic headache
Use only for alert patients > 15 years with a new severe headache peaking within 1 hour. Do NOT use with a new neurological deficit, prior aneurysm / SAH / brain tumour, or chronic recurrent headaches (≥ 3 similar episodes over ≥ 6 months).
Age ≥ 40 years
Neck pain or stiffness
Witnessed loss of consciousness
Onset during exertion
Thunderclap headache (instantly peaking pain)
Limited neck flexion on examination
Evidence
Original publication
Perry JJ, Stiell IG, Sivilotti MLA, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. Derived and internally validated the Ottawa SAH Rule in alert patients ≥ 15 years with peak headache within 1 hour and no neurological deficit; the six-item rule was 100% sensitive for SAH.
JAMA, 2013
Open source
Validation
Perry JJ, Sivilotti MLA, Sutherland J, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache. Prospective multicentre validation: sensitivity 100% (95% CI 94.6–100%) with specificity ~13.6%, confirming the rule identifies patients who need investigation but does not by itself reduce imaging substantially.
CMAJ, 2017
Open source
Guideline
Use only within the strict inclusion criteria. A positive rule means SAH cannot be excluded clinically and warrants non-contrast CT (and, depending on timing and pretest probability, lumbar puncture or CT angiography); it does not diagnose SAH.
Last reviewed: 2026-09
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