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Ottawa Subarachnoid Hemorrhage (SAH) Rule for Headache Evaluation
Clinical decision rule to rule out SAH in alert patients with acute non-traumatic headache.
Ottawa Subarachnoid Hemorrhage (SAH) Rule for Headache Evaluation
Age >=40 years
Neck pain or neck stiffness
Witnessed loss of consciousness
Onset during exertion
Thunderclap headache (instantly peaking pain)
Limited neck flexion on examination
ResultRule negative
None of the six high-risk features are present, in a patient meeting the intended population criteria - SAH is effectively excluded without further testing.
- High-risk features present
- 0
When to use
- Alert, neurologically intact adults (>15y) with new severe non-traumatic headache reaching maximum intensity within 1 hour.
- Not intended for patients with prior aneurysm/SAH, known brain tumour, chronic recurrent headaches (>=3 similar episodes), or new focal neurologic deficit.
Formula
Rule is positive (cannot rule out SAH) if any of: age >=40, neck pain/stiffness, witnessed LOC, onset during exertion, thunderclap headache, or limited neck flexion on exam is present.
Pearls and pitfalls
- Designed to rule OUT SAH, not to diagnose it - a positive rule simply means further workup is required.
- Validated with ~100% sensitivity for SAH in the intended population; specificity is low.