Table 3 Ottawa Subarachnoid Hemorrhage rule [11]

For alert patients > 15 years of age with new severe non-traumatic headache reaching maximum intensity within 1 h

Not for patients with new neurologic deficits, previous aneurysms, SAH, brain tumors, or history of similar headaches (≥ 3 episodes over ≥ 6 months)

Investigate further if ≥ 1 finding is present

1. Symptoms of neck pain or stiffness

2. Age ≥ 40 years old

3. Witnessed loss of consciousness

4. Onset during exertion

5. Thunderclap headache (peak intensity immediately)

6. Limited neck flexion on exam