Interpretation
| Result | Meaning |
|---|---|
| 0 criteria | SAH ruled out |
| ≥ 1 criterion | Investigate (CT; LP or CTA if CT negative and > 6 h) |
Formula
Positive if any: age ≥40 · neck pain or stiffness · witnessed loss of consciousness · onset during exertion · thunderclap (instantly peaking) headache · limited neck flexion on exam
Clinical pearls
- Applies only to alert (GCS 15) patients ≥15 years with new severe atraumatic headache maximal within 1 hour. Exclude new neurologic deficits, prior aneurysm or SAH, brain tumour, or recurrent similar headaches (≥3 over ≥6 months).
- The rule is very sensitive but not specific (15%): a positive rule means "investigate", not "SAH likely".
- A non-contrast CT within 6 hours of onset, read by a qualified radiologist on a modern scanner, is ~100% sensitive and can stop the workup.
Examples
ottawa sah rule 32 yo sudden headache no neck pain no loc not exertional, not thunderclap, full neck flexionottawa sah 45F headache peaked in 30 minsah rule 28M thunderclap headache during exercise
FAQ
Who can the Ottawa SAH rule be used on?
Alert patients aged 15 or older with a new, severe, non-traumatic headache that peaked within an hour and who have no new neurologic deficits.
If the rule is positive, does the patient have SAH?
No. Specificity is only about 15%; a positive rule means investigation is needed.