🧠 Ottawa SAH Rule (Subarachnoid Hemorrhage)
The Ottawa SAH Rule is a high-sensitivity clinical rule to help exclude subarachnoid hemorrhage in alert patients with acute non-traumatic headache.
Ottawa SAH Rule (Subarachnoid Hemorrhage)
Age ≥ 40 years
Neck pain or stiffness
Witnessed loss of consciousness
Onset during exertion
Thunderclap headache (instantly peaking)
Limited neck flexion on exam
When to use
Apply only to those meeting entry criteria, then check the six items; any positive item means SAH cannot be excluded and mandates further workup (CT ± LP/CTA).
How it works
Six items: age ≥ 40, neck pain/stiffness, witnessed loss of consciousness, onset during exertion, thunderclap (instantly peaking) headache, limited neck flexion on exam. Rule positive if any item present.
Key points
- The rule is designed to be ~100% sensitive at the cost of low specificity — it rules out, it does not rule in, so a positive result is expected in many benign headaches. (original synthesis · not guideline verbatim)
- Entry criteria are strict: age ≥ 15, new severe atraumatic headache peaking within 1 hour, and a normal neurological exam.
- It does not apply to patients with neurological deficits, prior aneurysm/SAH/brain tumor, or recurrent identical headaches.
References
- Perry JJ, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013;310(12):1248-1255.
- Perry JJ, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule. BMJ. 2020;369:m1224.
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.