Neurology

Ottawa subarachnoid hemorrhage rule

Identify need for SAH investigation in a defined acute-headache population.

Intended population: Age ≥16, GCS 15, neurologically intact, new severe nontraumatic headache peaking within 1 hour, presentation within 14 days.

All responses must reflect a clinician's verified history and examination. An unassessed finding is not an absent finding.
A positive rule indicates investigation, not a diagnosis. This rule does not choose CT versus lumbar puncture/angiography or exclude other dangerous headache causes.

Age (years)

Meets every inclusion criterion above?

Recent head trauma, papilledema, focal deficit, prior aneurysm/SAH/tumor/shunt/hydrocephalus, recurrent similar headaches ≥3 over ≥6 months, or already investigated for this headache?

Neck pain or stiffness?

Witnessed loss of consciousness?

Onset during exertion?

Thunderclap headache (instantly reaching peak pain)?

Limited neck flexion on examination?

Sources and scoring references

Original Ottawa SAH rule refinement (2013) ↗Prospective validation and exclusions (2017) ↗

Implementation references reviewed October 28, 2026. Verify applicability and unusual or treatment-changing results against the linked references and local guidance.